Salvage of Submarine S-51 C.
APPENDIX
C. Salvage of Submarine 5-51
C . 1 . Collision
The salvage of USS 5-51 more than 40 years ago is a prime
example of raising a submarine by a combination of self-
and external lift. The Salvage Officer was faced with a
formidable task since the submarine was completely flooded
and the pressure hull open to the sea. Five feet of the
hull was buried in mud and clay which meant an additional
lift force was needed to break the bottom suction. There
were few divers available who had experience in deep salvage
work, and there were not enough submersible pontoons for the
required external lift. Many of the tools to be used under¬
water were inadequate, such as cutting torches, underwater
lamps, and tunneling nozzles.
This report amply demonstrates the importance of persever¬
ance and ingenuity. These attributes spelled the difference
between success and failure in this salvage operation.
Also demonstrated are the unexpected and unpredicted
problems which plague Salvage Officers. It is of interest
to note that the force required to overcome bottom suction
was recognized by the Salvage Officer. The account clearly
demonstrates how this force can be reduced by ship motion
or extending the time the lift force is applied.
The following report of the S-51 operation should be of
intense interest to a submarine Salvage Officer and, hence,
is treated in greater detail than the other salvage reports
in these Appendices.
USS S-51 was sunk by collision with the steamship CITY OF
ROME on the night of 25 September 1925. The S-51 was struck
just forward of the conning tower on the port beam which
opened the pressure hull to the sea with a gash 2-1/2 feet
wide by 12 feet high. The submarine sank immediately,
completely flooding all compartments. Ten crew members
managed to leap from the bridge or get through the conning
tower hatch and clear of the ship as she went down. Three
of these were rescued by a boat from CITY OF ROME; the
other seven were never seen again.
C.2. The Position
The position of S-51 was about 15 miles south of Brenton
Reef Lightship and about 14 miles east of Block Island,
resting at a depth of 132 feet.
C-l
Salvage of Submarine S-51 C.
The first divers arrived at the scene the folloujing day
aboard a small diving boat from the Newport torpedo station.
The first diver down found that the S-51 was lying on a hard
level bottom and listing approximately 13 degrees to port.
The keel was buried 5 feet deep in the clay bottom.
C.3■ Rescue Operations
The diver made a careful inspection along the deck and
found air escaping in moderate quantities through all hatch¬
es. These hatches were closed, but evidently not set up
from inside for the additional air pressure caused by the
flooding. The diver hammered on the hatches but got no
response; apparently all hands were dead. However, in the
absence of conclusive proof rescue operations were attempted.
Two floating derricks, one of 150-ton lift capability, the
other of 100 tons, were hired from a commercial salvage
company. It was assumed that if life existed at all on the
submarine it would be because one or more of the after
compartments had been isolated by the survivors. Ill i t h the
engine room and motor room free of water, it might be
feasible to lift the stern. However, if they were flooded,
the cranes would not be able to move the submarine. The
latter was the case and further lift from the surface was _
abandoned.
Had the derricks been able to lift the stern of S-51, they
still could not have brought it to the surface. The falls
of the cranes were too short and there was no way to hang
off the load to get another purchase. UJith the suspension
of rescue operations, the task of salving S-51 was
commenced under the direction of Captain E.O. King,
Commander, Submarine Base, New London, Connecticut.
C , 4. Estimate of the Salvage Situation
The salvage surface force consisted of the diving ship
USS FALCON, a minesweeper, converted to an ASR; USS VESTAL,
a repair ship; and three tugs used in positioning moors and
towing pontoons. In addition, submarine S-50 was used as
a model for divers to rehearse procedures they would perform
on the wreck.
It was decided to raise S-51 by restoring internal buoyancy
and adding external lift by use of submersible pontoons.
Computations revealed that the amount of buoyancy required
to lift the completely flooded hull was 800 tons.
A reserve buoyancy of another 25 percent was needed for .
breakout, and as a safety margin, making a total of 1000 -
tons.
C - 2
baiuage or bUDmanne b-bx L.
It was hoped that 35D tons of buoyancy could be restored by
sealing and blowing various tanks and compartments. This
would leave 650 tons of external buoyancy lift to be applied
by use of pontoons. To obtain this, eight pontoons with a
net lift of 80 tons each were to be employed.
A study of the hatches and piping systems of S-51, especially
those of the external ventilation system and its valves,
showed that the submarine was not especially suited to the
use of compressed air as a means of dewatering compartments.
The hatches were all designed to seat with sea pressure and
had little provision for holding an internal pressure.
A light strongback on each hatch was only capable of holding
a maximum three pounds of internal pressure over the ambient
sea pressure, about one-third of the amount required to
force water out. Under these conditions, it appeared that
pumps would be the answer; but here too, there was a
problem since the available pumps could only work against
a head of 80 feet and the job required a head of 132 feet.
In addition, the air compressors on the FALCON could only
deliver 150 psi against a back pressure of 60 psi. This,
plus the friction in the airlines, would reduce the net
effect of compressed air to about 70 psi. It appeared that
both pumps and compressed air would have to be used to
- dewater the compartments unless the hatches could be made
to withstand the use of compressed air alone.
Two 80-ton and two 60-ton pontoons, originally built for
use in F-4 salvage, were available at Norfolk and were
shipped to New York. These pontoons, designed for operation
in 45 feet of water, had to be reinforced with extra
stiffeners and braces. The New York Navy Yard commenced
construction on six more 80-ton pontoons of the same basic
design, but of heavier construction to meet the 132-foot
operating requirement. These pontoons were strong enough
to permit surfacing from 132 feet without rupturing. As
an additional safeguard against bursting, 6-inch spring-
loaded relief valves were installed at each end. These
dump valves were set to lift at a pressure of 5 to 10 psi
above ambient pressure.
C . 5 . Mooring Arrangement
liihen diving operations were undertaken, FALCON always
moored broadside to the wind and seas to form a lee for the
divers. UJhen these conditions increased, the repair ship,
VESTAL, was moved around to windward and anchored as a
breakwater.
C - 3
Salvage of Submarine S-51 C.
To assist in holding FALCON in position, it uias customary
to anchor two of the assisting tugs about 150 yards off the
windward bow and quarter, and run out two mooring hawsers
to each ship. In very bad weather, the tugs were anchored
in tandem to windward, the first tug holding up the second
one, and the second tug holding the line to FALCON. In
this manner, it was seldom necessary to secure diving
operations due to the weather. As a result of this procedure,
diving operations were doubled over ordinary practice and
the length of the job correspondingly shortened.
C.6. Commencement of Salvage Operations
Diving operations on S-51 commenced about the middle of
October. The first efforts were directed toward cutting
away the loop antenna, the submarine clearing lines, and the
radio antenna. This was necessary to avoid fouling the
divers in the submarine's overhead rigging. The gear was
cut with a special cutting hook attached to a line from the
surface.
The next step was to get reeving lines in place for the
pontoon slings. Dipping a wire line under the submarine's
bow and hauling it back and forth in a sawing motion was
first suggested. This method was not feasible for several
reasons. The depth of the water made the geometry of the
sling unfavorable for sawing and might foul the lines.
Also, the hard clay bottom did not lend itself to sawing
through 60 and 100 feet of the bottom which were the
positions for the slings. It was certain that by the sawing
action, the sharp bilge keels and the box keel would wear
through the cable very quickly. Finally, no diving work
could be undertaken while the sawing was taking place.
Therefore, it was decided to tunnel under the hull with
fire hoses which was difficult, but which would allow other
divers to work inside the submarine hull at the same time.
In sealing up the submarine's interior, it was intended to
make each main compartment entirely independent of all
other compartments, with regard to watertightness. The
value of this policy was demonstrated on the final raising
day. To accomplish this, however, required additional work,
and the sealing problem was especially complicated by the
supply and exhaust ventilation mains in the superstructure.
The supply main opened into every space except the battery
room, and the exhaust main ran from the battery to the
engine room. There was no possibility of closing the valves
from these mains in the torpedo room or the battery room.
Consequently, closing the main air induction valve and the
main exhaust valve in the periscope shears would not isolate
the compartments.
C-4
It was necessary, therefore, to seal each compartment
inhere the induction entered the hull.
Several days were spent in attempting to clear auiay the
obstruction in the engine air induction valve, but luithout
result. As the valve had to be closed, it became necessary
to remove the decking over the valve in the superstructure,
tear up the steel deck beams over the valve using a 6-inch
manila line to FALCON's uiinch for the purpose, unbolt forty
3/4 -inch nuts which held down the valve bonnet, break the
joint, and lift off the 300-pound bonnet. All of this
work was finished on 2 November. A piece of 1-inch steel
pipe, 3 feet long and much corroded, was found to be jammed
under the valve disk. This was removed and the valve closed.
Evidently this pipe had been left in the vent main during
construction and had washed into the valve by the rush of
water when S-51 sank.
Near the end of October, the first four pontoons arrived
on board the 100-ton derrick UNITED STATES. They were
brought directly to the wreck, but about an hour after
arrival the weather changed and it was apparent that the
derrick was in danger. It was immediately started for
Newport, where it arrived not much ahead of a gale that
scattered the salvage squadron. It was clearly evident
that derricks could not safely be brought out, and there¬
after the derrick stayed in harbor where she put the four
pontoons overboard and prepared them for towing.
IJJork on the first tunnel, at frame 46, was started on
22 October. The divers available had done most of their
diving prior to the loss of S-51 locating lost torpedoes;
consequently, they were experienced in using a washing hose
for digging. Tunneling was, therefore, not an entirely new
experience for them. A 2-l/2-inch fire hose with a 4-foot
pipe and nozzle was first used at a pressure of about
40 psi. The progress for the first day gave reason for
optimism, but thereafter, trouble was encountered. Instead
of the soft mud in which the divers had ordinarily worked
and which washed freely with a hose, it was found that
under a thin layer of sand and mud was a bed of hard blue
clay mixed with sand. The consistency of the clay was such
that a moderate water pressure had no effect on it. It
was found impossible to raise the pressure on the 2-l/2-
inch hose as the diver was unable to withstand the reaction
of the hose, and lost control. After the first day's work,
it was necessary to raise the pressure if any clay was to
be washed out. To facilitate this, the last length of the
fire hose was replaced by a 50-foot length of l-l/2-inch
hose with a pipe nozzle of the same diameter. UJith this
smaller size, the diver was able to hold up to 70 pounds
of pressure, which cut the clay when the nozzle was held
close.
C-5
Salvage of Submarine S-51 C.
-
Another problem was the fact that the clay and sand mere so
heavy that they mould not stay in suspension when cut, but
settled again in the tunnel. This feature mas aggravated by
the small size of the water jet which was unable to set
up any appreciable current in the tunnel as it advanced under
the boat. As a result, the diver was compelled, after
cutting ahead a short way, to turn his nozzle and wash all
sediment backwards out of the tunnel. Consequently, only
a small portion of the diver's time on the bottom was spent
in actual cutting ahead.
The weather conditions in October and November were such that
diving was not possible for more than two days in succession,
after which two or three days might elapse before diving
could be resumed. It was found, on returning after each
storm, that the bottom currents had either partly or
completely filled the tunnel with heavy hard-packed sand,
that had to be washed out before any new cutting was
possible.
These factors, complicated by an insufficient force of
divers, prevented driving a tunnel through during the autumn
operations. Several times success seemed near, with the
divers approaching or even toughing the keel, but each time
bad weather brought a halt. UJhen tunneling resumed, ^
practically all work had to be redone.
UJhile tunneling was being accomplished outside S-51, divers
were at work sealing compartments inside the submarine.
To seal off the motor room, two divers entered from the
engine room and closed all necessary valves, including the
ventilation valve. Later, they closed the motor room
door and sledged down the dogs. To discharge the water,
the drain valve in the forward bilges of the motor room was
opened, there being a non-return check valve on the bilge
suction. In the engine room a valve bonnet on the drain
line was removed so that water forced from the motor room
would discharge into the engine room, but not in the reverse
direction. To admit air, a bolt was removed from the top
of the motor room and the hole tapped out. A 3/4-inch air
connection was inserted for attaching the blowing hose.
A strongback was bolted over the motor room hatch to prevent
it from blowing open under internal pressure. UJhen air
was put in the motor room, considerable water was expelled,
then air started to blow out of the ventilation main in the
superstructure .
By questioning the survivors, it was learned that the drain
valve on the line in the motor room had been defective and
could not be properly closed. To remedy this problem,
the motor room door was opened, the drain line disconnected,
and the valve sealed with a pipe plug.
C-6
Salvage of Submarine S-51 C.
After the motor room door was re-secured, another attempt
was made to blow the compartment down, evacuating the water
through the disconnected drain line. After some minutes of
blowing on this occasion,the water began to lower in the
compartment. Then, one of the divers reported air escaping
through the ventilation valve, which chattered like a
relief valve releasing great gusts of air. Nothing further
could be done during the autumn operations on this compart¬
ment.
Attention was then directed to the control room. To seal
this compartment required substitution of two salvage
hatches for the regular hatches in the conning tower and
the gun access trunk. The original hatches were unable to
hold even a nominal internal pressure. In addition, there
were many smaller valves that had to be closed and two
watertight (LL/T) doors secured that led to the battery room
and engine room.
Handling the salvage hatches presented a problem. Each
hatch was made of l-l/2-inch steel plate and had a heavy
strongback with a bolt running through it. A long section
of 4-inch suction hose was attached to the hatch for draining
the compartment when air pressure was applied. Assembled,
^ the salvage hatch weighed about 700 pounds.
After a rehearsal on S-50, it became evident that the
salvage hatches could not be handled from FALCON. The
up-and-down surge of the ship would make it dangerous for
the divers. It was decided therefore to handle the hatches
from underwater on the submarine. For the conning tower
hatch,a heavy oak timber provided with an eyebolt was se¬
cured over the bridge where it plumbed the hatch opening.
The salvage hatch itself was handled by a half-ton chain fall
secured to the eyebolt. Using this procedure, the hatch
cover was hooked to the chain fall after it had been lowered
to the bridge of the submarine. In one dive, two men
accomplished this task. For the gun access trunk hatch,
another oak beam was placed over the bridge timber in line
with the center of the gun access hatch. The salvage
hatch was lowered from FALCON and guided down by a line
secured to the side of the gun access trunk. As the hatch
neared the submarine it was dragged over by the divers who
placed the suction hose in the trunk and fed it down until
the hatch was landed on the trunk. The divers then hooked
into the chain fall and took the weight off the surface
line. Considerable difficulty was encountered handling
this hatch because of the slope of the hull. However, two
divers managed to get it in place and secured in one dive.
C-7
Salvage of Submarine S-51 C.
When both hatches to the control room had been sealed, the
next job was to close and seal-up the internal watertight
doors. The most direct means of entrance to the control
room was through the gun access hatch. To open the hatch,
the following procedure was carefully rehearsed on S-50 and
then carried out on S-51. Divers proceeded to the gun
access trunk on the starboard side. The glass port was
smashed and the latch released by inserting a specially
twisted bar into the 4-inch hole. Also holding the hatch
was a l/4-inch wire which was cleared by use of a cutting
hook; the hatch then flew open. The divers later entered
the trunk and endeavored to squeeze through the small oval
hatch at its lower end, but it was too small for a diver
to negotiate. This route was abandoned in favor of bulk¬
head, watertight doors in the adjacent compartments.
Two divers entered the battery room (forward of the control
room) and moved aft towards the control room watertight
bulkhead door. However, passage was blocked by mattresses
and bunks and was too clogged for divers to attempt getting
through. Next, the divers attempted to enter the control
room through the after bulkhead door from the engine room.
Two divers tried this entrance but were unable to squeeze
through. A second pair of divers had to quit when their
underwater lamps burned out while they were in the sub¬
marine. A third attempt by entering through the engine ~
room door was successful. The two men got part way into
the control room and cleared away a bunk that had washed
into the compartment from the battery room forward. This
provided a relatively clear passage through the remainder
of the control room. By working forward cautiously to
avoid entangling lifelines and lamp cables, the divers
managed to reach the forward door. The area was jammed
with wreckage which had to be carefully cleared away
before the door was finally secured.
On a previous dive, one of the divers noted that one of the
air banks in the control room showed about 2000 pounds of
air. An attempt was made to open all of the Kingston
flood valves in the main ballast tanks in preparation for
blowing them down, but without success. When it was found
that the air motors would not operate the flood valves,
they were opened by hand. By this method it was possible
to rig the No. 3 port tank for blowing, as well as the port
and starboard tanks for No.'s 4 and 5 main ballast tank
group. All other ballast tanks were inaccessible due to
wreckage.
After rigging the flood valves open, the air manifold was
set up to blow down these three ballast tanks. Another
diver was stationed outside the submarine to observe the
discharge from the Kingston valves.
c-a
Salvage of Submarine 5-51 C.
Air was turned on in all three tanks at once, and the gage
inside the ship started to drop. The diver outside noted
that a stream of muddy water was being discharged from the
Kingston flood valve in each one of the three tanks. The
tanks were blown for about 30 minutes until the pressure
gage inside the submarine dropped so low as to render
further blowing inadvisable. All air valves were closed
and the diver came out. None of the three ballast tanks
had commenced discharging air, so none of them were dry.
It was estimated that all of them were from one-half to
two-thirds blown down.
A rubber hose was found at the after door of the control
room running from a connection in the engine room to the
ice machine located under the deck in the control room.
As this hose prevented closing the door, it was cut by the
divers and gagged on both sides of the cut. The divers
then closed the after bulkhead door of the control room
and dogged it shut.
A hose for blowing the control room was secured to the
connection provided on the salvage hatch already installed
and the air was turned on. After building up a pressure of
3 or 4 pounds in excess of the bottom pressure at the point
of discharge, air started to blow from the ventilation
valve, as in the case of the motor room. Efforts to seal
the control room were terminated for the rest of the autumn
operations .
About the middle of November, divers worked in the engine
room on the fuel oil manifolds, setting the valves and
rigging air connections to blow the contents of the tanks.
The after group of oil tanks was blown first, the contents
being discharged through a hose leading to the surface.
It was found that one tank contained water, all of which
was blown out until air discharged from the flood valves.
The connections were then shifted to blow the forward
group, which was completed a few days later. The forward
group contained some water in the discharge line before
oil was reached.
Prior to the above operations, in late October, an attempt
was made to lower the first pontoon. Divers passed
messenger lines of 21-thread manila under the stern of
S-51 which was clear of the bottom. The manila messenger
was used to haul a heavier line which in turn pulled two
1-inch wire lines. The pontoon was to be lowered with a
15-fathom shot of 2-l/2-inch anchor chain hung from each
hawsepipe. The chain was stopped off at the top with a
heavy bolted clamp. The wire hauling lines were secured
to the lower end of each one of the chains.
C-9
C-10
Salvage of Submarine 5-51 C.
It was planned to lower the pontoon from the surface using
a 6-inch manila line at each end. The pontoon was flooded
until nearly awash. In this condition, the pontoon tended
to submerge at one end or the other because of the free
surface effect. Some time was spent in adjusting with the
vent valves and the air connections on each end to make the
pontoon submerge evenly.
This effort was unsuccessful and it was decided to let the
pontoon flood until it had negative buoyancy and then
lower it to the bottom by the 6-inch manila lines. As the
pontoon went down the lowering lines parted and it sank to
the bottom. FALCON was a short distance from her normal
position over S-51 while these experiments were being made
in pontoon handling. Consequently, the pontoon missed the
submarine on the bottom and landed about 50 feet away. In
the meantime, the hauling wires under S-51 had slacked off
and had fouled around the submarine. It took several days
of work to clear the 1-inch slings and refloat the pontoon.
It was evident that the methods previously used in lowering
and handling pontoons in shallow water were not applicable
in the open sea.
FALCON proceeded to Narragansett Bay where in shallow
water, and using another pontoon, an attempt was made to
lower it without losing trim. When the pontoon had taken
in enough water to submerge, the loss of external water
plane and the free surface effect inside the pontoon
destroyed all longitudinal stability. The pontoon then
upended and dove for the bottom. Two solutions seemed
possible; one was to allow the pontoon to flood completely
at the surface and provide means of lowering it that could
stand the full load of 40 tons. The second was to deter¬
mine at what point the pontoon had taken in sufficient water
to reduce its internal free surface phenomenon, thereby
improving stability somewhat. If the pontoon was held
reasonably level by the lowering lines, one end would not
have a tendency to float up while the other end dropped
and took all of the load. It was felt that if such a
condition could be found, the pontoon could be completely
lowered without losing trim.
After some calculation and considerable experimentation in
Narragansett Bay, it appeared that with a negative weight
of 10 tons the internal free water plane was sufficiently
reduced to make the pontoon fairly stable, provided it was
not permitted to exceed a moderate inclination. To handle
the weight of 10 tons, a large safety factor was necessary
for the dynamic conditions and for the probability of
exceeding the designated weight while flooding. It appear-
^ ed that nothing less than a 12-inch manila line would be
satisfactory.
C-ll
Salvage of Submarine S-51 C.
By the time these experiments were completed, it was too
late in the season to make an actual attempt to place a
pontoon alongside S-51.
After the middle of November the weather became so bad that
diving was possible only at infrequent intervals. The
water became extremely cold. From 21 November until the
end of the month diving was impossible. Finally, on 3D
November, diving was attempted again. On this occasion,
two of the three divers sent down had to be hauled back
up because their air hoses froze from the moisture in the
air being pumped down to them. At this time, only four
o^ the original ten divers who had started this work were
still in condition to dive. An attempt was made to hire
civilian divers to augment the force, but only three men
were found who were willing and qualified to work on the
job .
Considering the unsuitability of the weather and the fact
that only 1 day in 10 or 15 could be counted on as a diving
day, it was decided to suspend operations for the winter.
The mooring buoys were removed by the Lighthouse Service
and two marker buoys were left at the site of the sunken
submarine. The pontoons were left moored to the docks at
the torpedo station, Newport, Rhode Island.
C.7. Resumption of Salvage Operations
To prepare for salvage operations the following year, a
diving school was set up at the New York Navy Yard.
Twelve divers were found physically qualified and commenced
training in a diving tank. They were required to learn the
use of various underwater tools and to perform tasks of
working with pipes, cutting out rivets and handling weights.
Also, a series of experiments was carried out to develop an
underwater cutting torch. The torch, which had been
provided by the NAVY when salvage commenced, had failed to
work .
The second year of salvage operations on S-51 commenced
late in April. Some difficulty was experienced in re¬
locating the wreck because the marker buoys had drifted.
The first job undertaken was to land pontoons alongside
the port and starboard quarters of the submarine.
Considerable difficulty was experienced in this endeavor.
Lines carried away and the pontoons sometimes came to rest
some distance from their intended position. They were
then either hauled into position on the bottom or refloated
and sunk again.
C -12
Salvage of Submarine S-51 C.
The newly developed underwater cutting torch was used
for the first time with success. UJhen the chains had been
hauled through the hawsepipes of the pontoons a predeter¬
mined length, the stud of a link would be burned out,
which then permitted a nickel steel toggle bar 40 inches long
and 3-3/4 by 3-3/4 inches in section to be slipped through.
This was then locked by a bolt on each side of the chain
link.
UJork was commenced on lowering a pair of pontoons for the
bow slings. The reeving line was passed under the bow,
but it kept slipping free due to the rise of the forefoot.
To remedy this, a diver was sent down to release the anchor
on the submarine. The shank of the anchor then functioned
as a preventer. The reeving lines pulled the 4-inch manila
through the tunnel and then the wire was hauled down.
However, the 4-inch manila parted when a strain was taken;
it had been cut by the bilge keel. Attempts to locate the
4-inch manila line were unsuccessful. The weather then
worsened and the increasing seas caused the pontoon moored
alongside FALCON to surge and crash against the sides;
finally it had to be cast loose and towed away. UJhen a
diver went down the next day, he found the wire reeving
line fouled on the bottom and this had to be cleared away.
To replace the 4-inch line that had been cut by the bilge
keel, it was necessary for the divers again to work
through the tunnel. UJhen all was in readiness to haul in
on the wire and thus heave the chain through the tunnel,
it was found that the links caught and held on the box
keel. In every instance that a strain came on the chain,
the first link would be brought hard up against the angle
of the box keel which hung about 16 inches below the hull.
This heaving by the tug eventually tore the winch loose
from the deck and the effort was halted. The pontoon was
brought to the surface along with the chains. The hauling
wire was carefully checked, then the chains removed from
the pontoon. The eye of the hauling wire was shackled in
to the chain and a special steel fairing installed to
streamline the connection. LUith this rig the first chain
was independently lowered and passed through the tunnel
under the keel without difficulty. The first bow pontoon
was lowered on the port side until it was about 20 feet clear
of the bottom and a pair of divers went down and checked
the position. The pontoon was then lowered the rest of the
way and the locking bar was inserted.
This method of handling the chains and pontoons was
considerably superior to lowering the pontoons with the
chain attached. The reason for the original method of
rigging resulted from the means of securing the chains in
the hawsepipes of the pontoon.
C -13
Salvage of bunmarine S-51 C.
This was a steel clamp made in turn halves, weighing about
300 pounds, and secured by four l-l/2-inch bolts. Such a
rig was extremely difficult to handle and probably could
not be secured without auxiliary rigging from the surface.
In shallow water, where a diver could work all day, such
means were feasible. In deep water, however, where divers'
time on the bottom was very limited, it was considered
best to shorten the work by securing a pair of chains to the
first pontoon, making up the clamps on the surface. How¬
ever, when the use of the cutting torch made possible the
removing of studs in the links and insertion of the locking
bar at any desired point, it became possible to eliminate
the clamps entirely.
Early during the spring operations, work was started to
seal off the ventilation main leading to the control room,
engine room and motor room. The motor room was attempted
first, as the ventilation line leading to this compartment
could be most easily reached. The deck of the submarine
just forward of the motor room was removed and the deck
beams cleared away with the cutting torch. Several days
followed while a succession of divers worked on unbolt¬
ing the induction flange. Several of the bolts were
inaccessible because of the close proximity of the engine
air induction valve. To remove this piece, a wire was
brought down and wrapped around the pipe and a strain put
on it from the surface, tearing it clear. The flange was
then cleaned off and the blank cover bolted in place. Air
was then applied to the motor room to see if it would hold
pressure. After blowing for about half an hour, a stream
of air bubbles came to the surface over the forward end of
the motor room. The leak came from an opening in one of
the butts of an upper plating strake on the starboard side.
Apparently, a poorly fitted butt joint had been made tight
during construction of the vessel by peening the edges of
the plates and thus sealing the overlapping seam. The
effects of corrosion and an internal pressure had caused
the butt edge to give way, creating a bad leak.
Divers were sent down with strings of lead wool and the
crack was calked with ordinary wood calking tools. Then
an air-driven chipping and calking tool was applied.
The work went very slowly as each time the trigger was
actuated by the diver air bubbles obscured his view.
Most of the work had to be done by feel. When the leaks
had been calked, air was again applied and the water driven
down a little further. Again, bubbles streamed from the
compartment; this time from the stern of the submarine.
Upon inspection, a large dent was found about 10 feet from
the stern in the tiller room. In this dent one rivet was
missing and another nearly pulled through, allowing air to __
escape freely.
C -14
Salvage of Submarine S-51 C.
Mk
The tiller room mas a small compartment aft of the motor
room and connected with the latter by a manhole about half¬
way down the bulkhead. It was evident that this manhole
was open and that the air in the motor room, having driven
the water down to the level of the top of the manhole, was
now escaping through the tiller room rivet holes.
A lead plug was cast to the size of the open hole and
fitted with a tapered oak cone driven into its base to act
as an expander. Uihen this plug was inserted in the hole,
the wood plug was brought up against the frame bar inside
and resulted in spreading the lead plug inside when the
diver hammered it home from outside.
To seal the partly pulled rivet, the diver drove soft pine
plugs into the open parts of the countersink so that the
wood was firmly jammed in. The wood was then trimmed to
prevent lines or cables chafing across it and possibly
starting the leak again.
The reason for the dent in the shell is not definitely
known. The location was far removed from all collision
damage and could not have been a result of the submarine
hitting the bottom. It is believed however, that one of
the vessels engaged in the original rescue operations
dropped anchor over S-51 and that the anchor had landed
on the stern, dented it and bounced clear.
The work of sealing the motor room leaks was completed
early in June, and the pressure again applied. No further
leaks appeared on the outside of the vessel in the vicinity
of the motor room. However, when the water level inside
had been forced down to the point where it reached the
shaft stuffing boxes in the bulkhead between the engine
and the motor rooms, air started to escape in considerable
quantity through the stuffing boxes into the engine room.
At this point, the motor room was about two-thirds empty.
It was only by sending all the air FALCON could supply into
the motor room that it was possible to drive the water
lower. The moment blowing ceased, the air below the shaft
lines would escape and the motor room refill to this level.
Inquiry of the officers on 5-50 brought out the information
that on all submarines it was impossible to keep interior
shaft stuffing boxes tight as the vibration due to the close
proximity of the engines quickly wore the packing to a
considerable clearance. No attempt was made to tighten up
the stuffing boxes since they were practically inaccessible
to a diver.
Having sealed up the motor room ventilation valve by
blanking it off, consideration was given to the same pro¬
cedure for the ventilation valves in the engine room and
the control room.
C -15
Salvage of Submarine S-51 C.
The main engine air induction valve, having had its bonnet
previously removed in the process of closing the valve,
was quickly sealed from the outside by bolting a steel
strongback across the valve body and pressing a heavy oak
block firmly down on top of the valve disk to hold it on
its seat.
The battery exhaust valve, which discharged into the engine
room, and the ventilation supply valve, which opened into
the control room, presented different problems. Both valves
were closed by their internal locking gear, but it was
known that this was ineffective. It appeared possible to
get at a section of the battery exhaust main in the
superstructure and blank it off. The line to the control
room was so covered by other pipes and structure as to be
practically inaccessible.
It was noted that each one of the compartment ventilation
flapper valves had a l-l/4-inch drain valve screwed into
its body just above the flapper disk. In the case of
the motor room, such a drain valve had previously caused
considerable trouble by leaking and had to be plugged.
It now appeared that through these drain valve openings a
cement mixture might be injected into the ventilation
valve bodies on top of the closed flapper valves, which,
on hardening, would permanently seal the valves closed.
To carry out this scheme, a special elbow, to get into
a confined space, was made on the repair ship, l/ESTAL, to
suit the drain valve connection in the control room.
This was tried on S-50. The door from the engine room to
the control room, which had been closed during the fall
operations, was undogged and reopened. Three divers were
sent down to install the cement connection, but found
conditions in S-51 were sufficiently different to prevent
installation. After modification, the fitting was finally
installed, but with great difficulty, as the water in the
control room was black from particles in suspension and
vision beyond 5 inches was impossible. The work had to be
done by sense of touch in a cramped space. Conditions
were so bad that a submarine lamp was invisible unless
held within a few inches of the diver's faceplate.
Meanwhile, experiments were being carried out on the l/ESTAL
to determine the best cement mixture. The primary require¬
ment was to obtain a cement that would harden in salt water.
The secondary problem was to obtain a cement that would
flow freely through 250 feet of l-l/4-inch diameter hose,
pass through a number of valves and fittings and still not
be too liquid to set firmly.
C -16
Salvage of Submarine S-51 C.
Several brands of commercial cement mere tried but their
hardening qualities in salt u/ater, except in very thick
mixtures, mere extremely poor. A special bauxite cement
was tried and found to be satisfactory. A mixture of two
parts by volume of this cement to one part of water was
found to be thin enough to permit flow.
For injecting the cement, a steel tank was constructed and
tested to 200 psi. The tank had a quick-opening hand¬
hole on top for filling, test cocks on the side for
determining the cement level, and a discharge connection
tapering from 3 inches to 1-1/4 inches at the bottom.
Using 200 feet of hose leading to the bottom and attached
to a piece of 12-inch pipe, a full-scale experiment was
carried out on the repair ship to test the apparatus and
the mixture. The cement was forced out by an air pressure
of 150 psi on the tank. Five hours after the pipe had
been injected with the cement, it was found that it already
had set moderately hard. It was kept submerged in salt
water and by the next day had set solidly.
The hose and the apparatus were taken out to FALCON where
the divers ran the hose inside the submarine and connected
the last short length to the fitting on the control room
ventilation valve. lUhen all connections had been made,
the cement was mixed on FALCON and two charges forced
through. The divers then uncoupled the hose section near
the control room and sent it up. A few days later the
divers closed and dogged the door to the control room.
In the engine room a similar connection for injecting
cement was fitted to the battery exhaust ventilation valve
and a hose connected up for the job. Because this valve
was larger than the one in the control room, about 10
cubic feet of cement was used to seal up the valve. The
two ventilation valves in the control room and the engine
room were thus sealed off with only a fraction of the work
that would have been required by any other method. After
an hour of blowing the control room with high pressure air,
all water was expelled.
UJork was started on the tunnel for the last pair of pon¬
toons which were to be placed at frame 74, just even with
the conning tower. A new washing nozzle had been designed
aboard FALCON. In this nozzle were six jets, one large one
ahead, and five smaller ones radially astern. It was
found that this jet arrangement compensated for the
reaction which previously had made it impossible for the
diver to hold a 2-l/2-inch hose with adequate working
pressure. Also, the radial jets enlarged the hole cut by
the forward jet and shot the material back through the
tunnel .
C-17
Salvage of Submarine S-51 C.
The divers found that with this nozzle they could easily
control the hose at all pressures which the pump could
supply (200 psi) .
As a result of this highly efficient nozzle, a sizable
tunnel was dug on the starboard side, so that on the first
day the keel was reached in only five dives. The next day,
a tunnel was started on the port side. The fourth diver
washed his way into the starboard tunnel. He then crawled
through the tunnel with the messenger line. By the after¬
noon, two 2-l/2-inch chains were hauled through ready for
attachment to the pontoons. The efficiency of the new
nozzle was well proven in 2 short working days; the
previous tunneling work had required nearly 8 weeks.
After the last pair of pontoons were lowered and connected
to the chains, work was commenced on blowing dry the port
ballast tanks. These had been partly blown the previous
November using the submarine's air. On this final blow,
the air was supplied by a diver inserting an air hose from
the outside of the ship through the Kingston valves which
had been opened. These valves were buried in the clay on
the port side and it was necessary to wash them clear.
When blowing started, it was discovered that only a few
minutes of operation was required since most of the air _
in the tanks had been retained from the blowing operations
of the previous year.
To blow No. 2 port ballast tank, it was necessary to burn
a hole in it near the bottom since the operating gear for
the Kingston valves could not be reached from inside the
submarine. When air was applied to this tank, it was
found to leak through plates damaged when the submarine hit
the bottom. Consequently, the No. 2 starboard ballast tank
was not used as it would give the submarine a permanent
list when raised. It was also decided at this point not
to blow the other starboard ballast tanks for the time being.
The submarine had a list of 11-1/2 degrees to port which was
hoped would be eliminated; at the same time it was hoped
the bottom suction would be broken when the submarine rolled
to starboard. Having blown dry three portside ballast
tanks, the rolling moment available was somewhat over 600
foot-tons. It was believed that when S-51 was further light¬
ened, she would roll to starboard.
Consideration of the conditions governing the forward and
the after groups of oil tanks led to the conclusion that
the forward group of tanks could not be safely blown dry
while on the bottom. This was due to the fact that no
adequate vent for this group of tanks could be provided
which would relieve the pressure when the vessel rose.
C-18
Salvage of Submarine S-51 C.
This might result in rupture of the tanks. On the other
hand, this group could not be blown dry and then vented
before rising because the battery compartment directly
above it was open to the sea, and the tank top would col¬
lapse if the pressure inside the tank were reduced with the
vessel on the bottom. It was therefore decided that the
forward group of oil tanks would remain flooded while on
the bottom and these would be regarded as reserve buoyancy
available when needed.
Having blown the after group of oil tanks, the fuel oil
manifold in the engine room was set for blowing the forward
group. The ladder in the engine hatch was removed and the
floor plates under this hatch were taken out so that the
suction pipe from the salvage hatch could reach to the
bilge 4 feet below the floor plates. The divers had con¬
siderable difficulty in aligning the salvage hatch due
to the submarine's port list.
C . 8 . Initial Lifting Attempt
On 13 June, S-51 was completely sealed up. The motor
room was then dewatered as was the engine room, the two
being connected through the drain line. In preparation
for lifting, all pontoons were supplied with enough
positive buoyancy to float above the submarine. It was
necessary to level them off with equal amounts of chain
scope and to lash the slings. It was essential that the
pontoons be level before lifting commenced, otherwise
attainable buoyancy would be lost. The lashings were to
prevent the chain slings from slipping aft when the stern
was lifted on breakout. Ulhen this leveling operation was
attempted on the first set of pontoons, considerable
difficulty was experienced. They tended to upend as when
they were lowered from the surface. This was resolved by
lightening up one pontoon to the extent that a wire from the
surface could lift it to the proper level above S-51's
main deck. Then the pontoon on the opposing side was blown
until it rose into position and leveled. Ulhen the pontoons
were in proper trim, air was added to give them a positive
buoyancy of about 8 tons.
The lifting wire to the first pontoon was then cast free.
Leveling and positioning each set of pontoons was done in
the same manner. On three occasions, the lifting wire
parted allowing the pontoon to sink and the process had
to be repeated. Such operations were confined to
relatively calm sea states to prevent cables from parting.
Five days passed after blowing the portside ballast tanks
and S-51 had not rolled to starboard.
C-19
C-2Q
Salvage of Submarine S-51 C.
During this time the blowing hose to the engine room was
severed by one of the pontoons when it was being adjusted,
allowing the compartment to refill. The pontoons adjacent
to the battery room and control room were blown dry in an
attempt to initiate rolling the submarine, but nothing
happened. The fallowing day the stern pontoons were made
slightly buoyant, and a diver went down to install the lash¬
ing clamp. Soon after the diver started his descent, the
tenders topside observed air bubbles railing the sea the
entire length of the submarine. UJhen the diver had reported
on the bottom, he sent back word that S-51 had shifted and
now was nearly 20 degrees to starboard.
This news greatly heartened the Salvage Officer.
There could be no doubt that the suction effect was in a
large measure broken by the roll. It was also discovered,
on further inspection, that the stern of S-51 had lifted
about 5 feet, showing that the buoyancy already attained
astern was nearly sufficient to start the stern upward
without help from the stern pontoons. This checked out
well with the buoyancy calculations. These had been
revised to reflect that a large portion of the tiller room,
all of the motor room, most of the engine room and several
fuel oil tanks had been dewatered. The buoyancy calcula-
_ tions are shown in Table C-l.
UJhile the leveling operation was underway, starboard
ballast tanks 3, 4 and 5, which had never previously been
dewatered, were blown dry. A diver then descended to
inspect the location of the starboard after pontoon, which
was somewhat close under the counter with the submarine
leaning on it. The diver was standing on the bottom just
outboard of the pontoon when it rolled gently and then
started to float up while the submarine rolled from 20
degrees starboard to 10 degrees port. The diver reported
this topside and then, as it appeared that the submarine
and pontoons were on their way up and that he was in a
dangerous position, he started to run along the bottom to
get well clear. Unfortunately, his air hose led across the
pontoon chains and was fouled there. The diver then
climbed his air hose to the floating pontoon and cleared it.
Shortly after this, the pontoon settled again, coiling
down the chain under it where the diver's air hose had
been snagged.
To prevent any premature rise of the stern, about 60 tons
of water were flooded back into the third pair of pontoons,
abreast of the conning tower. An inspection made shortly
after showed that the stern, which had been up about 5 feet
or more, had settled back nearly to its original position.
The submarine was now heeled 5 degrees to port.
C - 21
C-22
TAB C-l
BUOYANCY CALCULATIONS
Compartment |
Total Buoyancy |
Expected |
Actual Net Buoyancy |
Control Room |
90 |
54 |
60 |
Engine Room |
110 |
88 |
96 |
lYlotor Room |
137 |
104 |
137 |
Port Ballast Tanks, |
62 |
46 |
50 |
Starboard Ballast Tanks |
62 |
46 |
50 |
After Group Oil Tanks |
33 |
23 |
33 |
Forujard Trim Tank |
10 |
8 |
10 |
Hater Round Torpedo Tank |
6 |
4 |
6 |
No. 2 Bow Buoyancy Tank |
11 |
8 |
11 |
Total |
521 Tons |
381 Tons |
453 Tons |
C-23
Salvage of Submarine S-51 C.
Lashing the pontoons as they leveled off was done partly to
hold them against a change of position during the bloiring
operations, but mainly to prevent them from slipping aft
when the stern lifted and before the boiu came up. It
was essential to ensure that the bow pontoons, in particular,
did not slip, otherwise they would lose their lifting
moment and allow the stern to broach at a steep angle,
possibly tearing out the stern slings. If such an event
happened, it would destroy months of work, in addition to
being extremely dangerous. Wherever possible, appendages
of the submarine were used for lashing preventers. The
stern pair of pontoons had the after chain passed inboard
of the shafts, just forward of the skeg. The bow pontoons
had the forward chain caught in the anchor well under the
keel and the after chain rove through the bow plane guards
so that movement was impossible (Figure C-l).
To prevent motion aft on the part of the second and third
pair of pontoons, a special steel clamp was secured on each
chain below the pontoons and just above the point where
the chain cleared the hull. A 1-inch wire lashing with
an eye in each end was then run generally athwartships
just above the deck of the submarine and attached to the
special clamps. The entire rig was designed for a breaking
strain of about 35 tons on each wire. In this way, each —-
wire tightly cradled the submarine in a continuous loop of
chain and wire when the angle of the ship caused the wires
to take up a strain. Further, the wires for the third pair
of pontoons led across the deck just forward of the gun
access trunk (Figure C-l), which thus acted as an effective
stopper. As an additional safeguard for this pair, another
wire was led around the gun mount somewhat forward of the
pontoon.
To keep the second pair of pontoons from sliding forward,
a wire lashing was run from the chains aft around the gun
mount, in addition to the athwartships pair of wire
lashings. It was further evident that under full buoyancy,
the bilge keels in way of the chains for the second and
third pair of pontoons would buckle up and thus form a
niche for these chains which would tend to prevent slippage.
Having secured the lashing clamps around the chains, the
divers took measurements of the lengths of lashings needed,
using a small manila line stretched between the clamps.
11/ith these lines as a guide, FALCON cut the 1-inch wire
and spliced in eyes with cable clamps.
During the installation of the lashing wires on the second
pair of pontoons, trouble commenced which led indirectly
to the rising of the bow a short time later. m
C-24
Salvage of Submarine S-51 C.
When the second pair of pontoons had been leveled off with
moderate positive buoyancy, measurements for the lashings
were taken. When the lashings were sent down for installa¬
tion, it was found that they could not be installed because
the forward end of the No. 2 starboard pontoon had sunk
until it rested on the bow pontoon just ahead of it. The
bow pontoon was on the bottom and had not been floated up.
Had this bow pontoon not been there, the No. 2 starboard
pontoon would have sunk to the bottom, probably standing
on end. Inspection revealed that the pontoon had sunk be¬
cause of many small leaks emanating from seams and rivets.
These leaks were probably started by the knocking about
that the pontoon received during towing and while along¬
side FALCON. Every pair of pontoons leaked to some extent
except the third pair. The result of this condition was
serious. Considerable effort had already been expended in
leveling off the pontoons and it was necessary that they be
kept leveled off. The starboard pontoon was refloated and
thereafter all pontoons were given periodic shots of air
to compensate for the leakage.
On 20 June, the bow pontoons were leveled off and the
flood valves closed to minimize flooding due to the small
leaks. The next day the divers were down measuring for
_ lashings on the stern pontoons when the stern pontoon on
the port side suddenly shifted and lifted the stern about
10 feet. Fortunately, the divers escaped injury. The
forward end of this pontoon was given some air to replace
what had been lost through leakage and an attempt was made
to close the flood valves, but only one could be partly
closed. Since the submarine was considered to be light, the
engine room was flooded to prevent a premature rise. The
final lashings were put in place by the end of the day
on 21 June.
The next day was stormy and divers could not be used, and
raising 5-51 was out of the question. Since it was known
that air leaked from the pontoons, FALCON moved into her
moorings and picked up the air hoses which were buoyed off
in the salvage area. The stern pontoons were blown first
for one minute, then the third pair of port and starboard
pontoons was given a half minute blow. Since the second
pair of pontoons had been blown dry previously and their
flood valves kept closed, they were not blown at this
time.
Problems arose when the hoses to the bow pontoons became
fouled in the propeller of FALCON. This required several
minutes to clear in the heavy seas. As the hoses were
brought aboard to be connected to the air manifold, the
■—- Salvage Officer observed a mass of bubbles breaking the
surface.
C-25
Salvage of Submarine S-51 C.
It was thought at first that one of the hoses had carried
away below, but the volume increased and became excessive
for such an accident. It was sensed that either the bow
pontoons had torn loose and were coming up, or the sub¬
marine itself was rising. In either case, FALCON was in
a dangerous position. The mooring lines to the stern were
on the winches and the winch men at the throttles in prepa¬
ration for unmooring. The port quarter line was cast off
and the starboard quarter line heaved in full speed to haul
FALCON'S stern clear. The ship was barely out of the bubbles
when in a cloud of spray the bow pontoons burst through the
surface followed quickly by the second pair, with the bow
of S-51 visible between them. FALCON let go her port bow
mooring lines to be clear of the area where the stern of the
submarine would come up. Meanwhile, the four pontoons hold¬
ing the bow of the S-51 surged in the waves, smashing into
one another. It was decided to commence blowing on the
stern compartments and pontoons to complete the floating of
S-51 and make for sheltered water.
To furnish sufficient air to all spaces in the blowing
process required more than 2 hours. An attempt was made
to use air from S-50, but the rough weather prevented the
submarine from coming alongside. The steep up-angle of
S-51 prevented the dewatering suction hoses on the salvage
hatches from reaching the water, which was mostly at the
after end of the compartment. It was determined that about
130 tons of buoyancy in the control room and engine room
were lost because of this. When air bubbles were seen on
the surface over the middle of the wreck, it was obvious
that the stern was not going to come up.
About noon, a sizable bubble appeared over the stern.
At first it was thought the stern was coming up. Then the
bubbles increased and the starboard after pontoon broke the
surface, followed in a few seconds by the port after pon¬
toon. The 2-l/2-inch chains had parted under the submarine.
It was now impossible to raise the stern with the loss of
buoyancy of the after group of pontoons. There was
immediate danger of the four surfaced bow pontoons sinking
as they crashed into each other in the heavy seas. Since
all floods and vents on these pontoons were closed, it was
necessary for a man to swim to each one and open the valves.
When this had been done and S-51 had settled back to the
bottom, FALCON unmoored and took refuge from the storm.
The pontoons that had broken free from the stern were
taken in tow to port.
C-26
Salvage of Submarine S-51 C.
C.9. Successful Lift Made
The next day two divers were sent down to inspect the
results of the accidental raising of the bow. The bow of
the submarine was about 30 feet from the original position
and the pontoons were scattered on the bottom on their
ends, with chains and wires in a tangled mass.
A study was made to determine the cause of what had happened.
It was concluded that the bow pontoons must have been more
buoyant than estimated. There was no means of knowing the
buoyancy condition of a pontoon unless it was completely
empty or completely full. It appeared that sufficient
buoyancy had accumulated forward when work ceased late on
the previous day. Surfacing at that time was probably
prevented by the suction effect of the clay bottom. The
air put into the tanks just prior to the surfacing was
either aft or amidships and would have had negligible
effect on the forward lifting moment. The air in the after
pontoons would tend to reduce the forward moment by shifting
the center of buoyancy aft, and would help hold the bow down.
It is probable that the motion of the sea was sufficient to
rock S-51 in her bed on the bottom. Such motion at that
depth had been observed previously by divers in the sway¬
ing back and forth of the pontoons afloat over the hull.
On this occasion the lightened ship was rocked sufficiently
to break loose the suction on the bow, which rose with
accelerating force. The air in the pontoons expanded as
they rose, increasing the buoyancy.
The first job attempted when the divers had returned was
to place a pair of reeving lines under the submarine for
replacing the second pair of pontoons. The keel was barely
touching the bottom and it was essential to get the lines
under before it settled. One line was passed through at
frame 30 and sawed back to frame 42 by two divers. For
the second reeving line, a tunnel had to be washed which
took about half an hour using the new nozzle. Messenger
lines, then wires, were passed to pull chains into position
which were laid out on the bottom until needed.
The next step was to clear away the pontoons at the bow.
One pontoon was still afloat and fouled by one of the
lashing wires across the deck; it was cut loose. This
was done by a diver with the cutting torch. UJhen the
pontoon swung back in position, it swept the diver off the
submarine, but he miraculously escaped injury.
UJhen all of the pontoons had been freed and surfaced, they
— were taken into port for repairs. The seams were calked
and the wood sheathing replaced.
C-27
Salvage of Submarine S-51 C.
By early July, FALCON was again over S-51 ready to lower
pontoons. The same procedures were employed in connecting
the sling chains and leveling the pontoons above the main
deck of the submarine.
Certain forward tanks, which on 21 June were dry, were on
this occasion left flooded. The No. 2 bow buoyancy tank
was considered lost as it was dented in and could not hold
air pressure. The capacity of the tank was small and did
not warrant the extensive work required to repair it.
The forward trimming tank and the water-round torpedo tanks
had vented themselves down practically to atmospheric
pressure while the bow was at the surface. On sinking
again, these tanks reflooded under the bottom pressure.
Had time permitted, they would have been blown down again,
but the weather forecasts for the following day were such
that it was considered unsafe to risk further work which
would delay the job until a later date. Work on these
forward tanks was abandoned with regret.
Another consideration causing some anxiety was that about
150 tons of buoyancy in the six forward pontoons would be
unavailable for lifting the bow while the stern was up.
This was because the pontoons would assume the angle of the
ship, about 25 degrees, and only half of the pontoon could
be blown down. It had originally been intended to ensure
this buoyancy by blowing the after halves of all six for¬
ward pontoons before lifting the stern. However, with the
experience of 22 June in mind, this plan was abandoned.
No chances could be taken that would permit the bow to come
up first again. Confirming the soundness of this calculation,
the last two divers up reported that S-51 had changed her
list position from 20 degrees starboard to nearly upright
or just a few degrees to starboard. It was clear that the
submarine was moving with slight or no suction holding her.
The margin of positive buoyancy for starting the bow up
after the stern had surfaced was not great, but it was
thought to be adequate. The Salvage Officer kept in mind
the forward group of oil tanks that could be blown if need
be, although there was some risk of rupturing the tanks.
HJhen the last diver had left the bottom, FALCON hauled
clear, leaving S-51 about 150 feet away on the port beam
and parallel to FALCON. The mooring buoys ahead and astern
were dragged clear to afford an approach for the tug,
SAGAMORE, which steamed in ahead and picked up both the
buoyed-off bow towing lines to S-51. The other tug, IUKA,
came in from astern to take the other towing line.
The starboard mooring buoy was dragged clear so that the
assisting submarine, S-50, could move in to furnish air
from her banks.
C-28
C-29
Salvage of Submarine 5-51 C.
Shortly after noon, the compressed air urns applied to the
engine room and motor rooms. After blowing for an hour,
air started discharging at the surface over the engine room
hatch. Blowing was maintained for a few minutes longer to
ensure that both compartments were dry. The air pressure
was then shifted to the control room and almost immediately
air was seen escaping at the surface. This was a serious
situation. It could only indicate that the control room
was losing the air rapidly, or that the hose had carried
away. No examination could be made as FALCON was not in
diving position over 5-51; and, in any case, with S-51
partially buoyant, diving would be too dangerous both to
FALCON and to a diver. It had to be assumed that 60 tons
of buoyancy were lost through the control room reflooding.
After blowing the stern pontoons for only 11 minutes, a
large bubble mass appeared, followed shortly by the stern
pontoons containing the stern of S-51 in the chain slings
below the surface. All air was immediately sent to the six
forward pontoons; blowing was continued on them as a group
for about 40 minutes when several air discharges at various
spots forward showed that some of the pontoons were dry.
(Tleanwhile, air was shutoff on all six bow pontoons and
then re-applied to them one-at-a-time to test their
condition. It was found that both the bow and third pair
were venting air from forward and after ends. It was also
found that the after ends of both pontoons in the second
pair were venting air and were therefore also completely
blown down. There remained only the forward ends of the
second pair to be blown. All air was now concentrated on
the two hoses leading to the forward ends of the second
pair of pontoons. The situation was tense, as nearly an
hour had gone by since the stern rose. Blowing was
continued at a reduced speed and still pressure showed an
increase on the second pair, indicating they were still
forcing water out. Then the gages showed a pressure drop
on the bow pontoons. The surface of the sea became
turbulent and within a few minutes all pontoons were riding
on the surface. The air was put on the forward group of
fuel oil tanks which were blown clear, giving additional
buoyancy.
C . 1□ . 5-51 Under Tow
Boats went alongside the pontoons and secured the flood
valves and cleared the blowing hoses to FALCON. Late in
the afternoon the towing operation got underway. IUKA
led with a 100-fathom line to S-51. A preventer was secured
between the bullnose of S-51 and her gun mount. —>,
C-30
Salvage of Submarine S-51 C.
FALCON brought up the rear with her air hoses to the tanks,
compartments, and pontoons. A 150-fathom line from the stern
of S-51 to FALCON was used to prevent FALCON from dropping
too far behind and parting the air hoses. An independent
10-inch manila line was run directly from FALCON’s bow to
SAGAIY10RE. FALCON was thus towed and was able to steer S-51
by use of the line to her stern.
The only part of S-51 which was clear of the water was the
signal bridge of the conning tower. The periscope shears
indicated that she was listing about 10 degrees to star¬
board. Maximum draft of the submarine was about 33 feet;
this allowed a safe margin through all channels encountered
and into drydock. It had been anticipated that the
minimum draft throughout the tow would be 35 feet.
The first stage of the tow was on a course direct for
Point Judith to get over shoal water as soon as possible.
Towing speed varied between 2 and 3 knots. FALCON main¬
tained air pressure on the hoses to counteract any addition¬
al flooding.
The tow proceeded satisfactorily until reaching the East
River. Here, after passing Blackwells Island and only
about a mile from the Navy Yard in Brooklyn, S-51 grounded
on lYlan-of-Uiar Rock. The second pair of pontoons broke loose
as a result, and considerable effort was required in
shortening slings on the remaining pontoons in order to
refloat the wreck.
On 8 July, S-51 crossed the sill of the drydock in New
York, 9-1/2 months after her sinking. The actual salvage
time required to raise the submarine and bring her into
drydock was 124 days.
C - 31
C-32
C - 3 3
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