22-1. The problem of escape and rescue of personnel from sunken disabled submarines is currently undergoing review and study by the Navy Department. As projected submarines will be capable of operating at depths greatly in excess of 500 feet, it is evident that currently available escape devices, rescue chambers, search aids, and doctrine for their proper use, must be reconsidered as to their applicability for use at such depths. This is particularly apropos in view of the tragic war experience of Tang (SS306) where only six of some forty men were able to escape from underwater although the submarine was sunk in only 180 feet depth.1 It has become apparent that new devices and techniques must be developed before escapes from submarines disabled at relatively great depths will be feasible.
Submarine Escape Notes
22-2. There are at present but three accepted methods considered practicable for our submarine service by means of which personnel can successfully transit from a sunken disabled submarine through the intervening water layer to the surface. The first and most obvious method is based on rescue by the use of a structural chamber designed to withstand hydrostatic pressure throughout its operating depth and which can be brought down from the surface to specially designed hatch openings on the disabled submarine below, enabling relatively safe group escape. This instrument was developed by the U.S. navy and is known as the "submarine rescue chamber". The second method calls for individual escape, personnel exiting from the disabled submarine through either a small intermediate enclosed air-lock or a skirted-type trunk built into the pressure hull, and then slowly ascending to the surface with the aid of a mechanical breathing deice known in the U.S. Navy as the "lung". Rate of rise to the surface of the escaping personnel using this second method is regulated by ascending a line secured from the submarine to a surface buoy. An escape breathing apparatus has been used by all major navies and in the U.S. Navy a certain amount of "lung" training under simulated escape conditions is normally a mandatory requisite for all submarine service candidates. The third method may at the present time be considered an emergency variation of the second method. Individual escape is made through the same air-lock or trunk as in the second method but ascent to the surface is "free"; i.e., a rapid ascent is made without the use of mechanical breathing aids or ascending line of any nature, escaping personnel rising under the influence of their own buoyancy and swimming up. Although some instruction is given in this method of escape in the U.S. Navy, it has so far not been particularly emphasized or recommended and "free" training ascents have not been required due to preference for the "lung" escape and the probable training hazards involved in "free" escape where large numbers of men are involved.
22-3. The escape problem on submarines in considerably increased by the necessity of having to confine escape structures and equipment
to those consistent with the required military characteristics of the ship. Space and weight considerations usually render it extremely difficult to achieve even the minimum desired military features on a new submarine design. Escape provisions are therefore naturally given secondary emphasis. Many workable schemes which would be decided improvements over existing escape arrangements could be devised if a submarine had no military mission. One such ideal but inadmissible proposal would be to design a portion or portions of the hull which could be detached and brought to the surface by the surviving members of the crew.
22-4. In the entire history of the U.S. Navy there are only two known instances of successful underwater escapes fro sunken disabled submarines.
(SS192) sank of the Isles of Shoals in 230 feet of water on 23 May 1939, when all compartments aft of the control room flooded through the engine air induction piping. The next day all of the 3 men who survived the initial flooding were removed through the forward torpedo room escape trunk by expeditious and skillful use of a submarine rescue chamber. The task was accomplished in four trips. Tang (SS306) was sunk off the coast of China in 180 feet of water on 26 October 1944 by the malfunctioning of one of her own torpedoes. Six men made successful individual escapes from underwater, one from the conning tower and five from the forward torpedo room escape trunk. The conning tower escape and one of the forward torpedo room escapes were "free". The remaining four were "lung" escapes. At least eight other men are known to have left the escape trunk but either died shortly after reaching the surface or were not seen again after leaving the trunk.
22-5. Since the experience of the U.S. Navy with underwater escapes other than training exercises, is limited to the above two cases, it is necessary to turn to the experiences of other nations for further data. The British Admiralty Submarine Escape Committee has compiled information and statistics on every instance known to them of past submarine escapes of all countries. These records contain much interesting, and in some cases, detailed information. They serve to stress the difficult conditions usually attendant upon submarine escapes after damage and which in most instances have prevented a high percentage of successful escape completions. The escape problem on submarines can be considered in three phases as follows: (1) survival within the submarine after damage up to the time personnel actually exist from the hull, (2) survival during the ascent to the surface and (3) survival after reaching the surface until rescued.
22-6. According to British records, of all the personnel who have been carried to the bottom in known cases of sunken submarines, a total of about 500 men are believed to have survived both the initial accident or damage causing the sinking and the subsequent primary flooding. Of these 500 men, a total of 32 were rescued from three submarines of such small size that the boats were lifted bodily by cranes;2
33 were saved by rescue chamber;3 and 46 were taken off a submarine sunk in shallow landlocked waters where raising the bow of the ship was comparatively simple and expeditious.4 Of the remaining 390 men who survived the initial accident, approximately 250 or 60% perished inside their respective submarines. It is probable that the principal cause of the majority of these deaths was CO2 poisoning, in some cases due to delaying the escape attempt too long,5 and in others to the accelerated poisoning effect of CO2 when present in atmosphere under high pressure.6 This latter condition occurs when flooding a compartment to equalize internal pressure with sea pressure to permit a skirted-trunk escape. Other known causes were drowning due to further uncontrollable or inadvertent flooding,7 drowning as a result of deliberately flooding a compartment to equalize internal pressure with sea pressure to permit skirted-trunk escapes,8 chlorine gas,9 and drowning with an air-lock type escape trunk.10 Of the 142 men who are known to have left their submarines on attempted individual escapes, 106 men or 75% reached the surface alive and survived until rescued. This represents only 27% survivors of the possible original 390. Of the 36 who left their ships on attempted escapes but did not survive, some are known to have reached the surface alive but subsequently died by drowning, exhaustion, or by prolonged immersion in cold water.11 The others died from various causes, among them being air embolism, asphyxiation, ruptured lung tissue due to failure to exhale during ascent, and drowning due to inhalation of water during ascent.
22-7. The statistics for these escapes, although not based on enough instances to be conclusive indicate the following interesting and pertinent points:
(a) It appears that with present equipment and techniques the chance of survival by using the individual escape method decreases about 10% for every 30-foot increase in depth, until a 250 feet and beyond, the chance of survival is very small.
(b) The phase between the initial accident and the actual escape attempts is by far the most critical. Eighty-eight per cent of all subsequent deaths among personnel who survived the initial accident occurred during this period.
(c) The advantage of rapid flooding over slow flooding when sea water must be admitted to a compartment to equalize internal air pressure with external sea pressure to permit escape through a skirted-trunk, is demonstrated by the fact that there were only 21% survivors after slow flooding whereas 66% survived when flooding was rapid. As would be expected, the figures also show that as the depth increases, a higher percentage of survivors results when the escape compartments are flooded rapidly rather than slowly. This is particularly marked at depths greater than 100 feet.
(d) The hazard of the ascent itself, particularly when made by well trained personnel, is relatively minor for depths up to about 200 feet. Of all the men who left their submarines on individual escape attempts, either with or without an apparatus, probably less than 10% perished during the actual ascent.
(e) Well over half of the survivors made "free" ascents, either entirely without breathing apparatus or with such apparatus but using it as a buoyancy bag only due to maloperation or defective parts.
22-8. When circumstances permit use of a submarine rescue chamber, this method is usually to be preferred since it is likely that a higher percentage of successful rescues will be obtained and no individual effort is required on the part of the men trapped within the sunken submarine. However, the following conditions must exist:
(a) The fact that the submarine has sunk must be made known to cognizant rescue authorities within a short period after the sinking occurs.
(b) Its exact position on the bottom must be definitely established.
(c) The depth of water must not exceed the operating depth of the rescue chamber, or with present apparatus, the depth at which divers can descend to attach a downhaul cable.
(d) A rescue chamber, trained crew ad rescue vessel must be so located as to reach the scene quickly.
(f) The survivors within the submarine must be able to reach an escape station fitted for use of the rescue chamber.
(g) List and trim of the submarine as it lies on the bottom must be such as to permit proper access to the escape station attaching surface.
In time of war, conditions (a), (b) and (d) will usually not be met.
22-9. Presently available rescue chambers and operating gear are not considered suitable for rescue of submarine personnel at depths much exceeding 450 feet. This is due to the fact that, although the
structural design of the latest chambers provides for a rated operating depth of 450 feet, divers must attach the chamber downhaul cable to the submarine and 450 feet is considered to be about the maximum possible working depth of divers using present diving techniques under ideal conditions. Development is currently underway on a proposed submarine messenger buoy which when released from a sunken submarine will float a light high strength rescue chamber downhaul cable from depths as great as 850 feet. Investigation shows that the present rescue chambers can be altered for use at 850 feet with but minor modifications. This scheme will eliminate the use of divers and the need for complicated mooring of the rescue vessel.
22-10. When use of the rescue chamber is not feasible, due to any of the conditions enumerated in paragraph 22-8 above, the only hope of survival for the crew members will then lie in individual escape attempts. The submarine escape device or "lung" was developed by the UI.S. Navy in 1929 to provide individual crew members with a reasonably safe means of escape from disabled sunken submarines. An extensive program of indoctrination and training of submarine personnel in its use, capabilities and limitations was undertaken. In order to provide "lung" training at substantial depths, escape training tanks were constructed at the U.S. naval Submarine Bases at New London and Pearl Harbor in 1930 and 1932, respectively. These towers have an overall height of 134 feet, providing a vertical column of water 100 feet high and 18 feet in diameter with escape locks or compartments simulating those on submarines located 18, 50 and 100 feet from the top of the tank. This permits escape training under conditions approximating those existing in similar depths at sea an with identical pressure factors. With the advent of World War II the program was expanded tremendously in an effort to provide "lung" instruction for all men training for the submarine service, although a considerable number of men unfortunately did not have access to such training. Since inception of the program, over 46,500 men have made the 18-foot ascent, over 29,800 men have made the 50-foot ascent and over 6,300 men have made the 100-foot ascent.
22-11. A study of Tang's experience, where only 5 men, or 10% of a possible 45 men trapped in the forward torpedo room, successfully escaped, indicates that an increase in the speed of operation of the trunk would have enabled more personnel to make the attempt. The average time between successive escape parties was from 45 minutes to one hour. This compares very unfavorably with recent shallow water escape exercises conducted by Sirago (SS485) on 28 and 29 August 1946. The submarine was submerged to a keel depth of about 70 feet and a total of 35 officers and men made individual escapes through the forward torpedo room air-lock, entering the trunk in groups of
3 and 4. The average time for each escape cycle, i.e., the time required for each party to enter the trunk, flood, escape, and for subsequent draining and readying of the trunk for the next party, was about 15 minutes. The minimum cycle time was 9 minutes and the maximum 26 minutes, this latter time including rigging of an escape buoy, ascending line, and streaming of a Mark 4 rubber boat from the escape trunk. During thee exercises three men experienced difficulty with their "lungs". One who had previous instruction in "free" escape made the ascent successfully without his "lung". The other two returned to the trunk.
12-12. The need for continued and rigorous "lung" escape instruction for all men and officers of the active submarine service, including periodic refresher courses, is clearly indicated if reliance is to be placed on this method in the future. In addition, more emphasis should be placed on the "free" escape method. Familiarity with this type of escape certainly holds the possibility of saving lives in many conceivable instances and will in addition induce more confidence in the "lung" type of escape.
22-13. It is pertinent to consider whether or not more lives would have been saved on Tang had the forward torpedo room been fitted with a skirted trunk, as in the after torpedo room, instead of the air-lock type escape trunk. In Tang's case, there are certain advantages which could be claimed for either type due to the fact that the depth of 180 feet was only slightly in excess of that beyond which the skirted trunk is ordinarily not considered suitable.
22-14. The principal advantage of the skirted trunk is that once the escape compartment has been flooded so as to equalize internal air pressure with sea pressure, and the trunk outer hatch has been opened, individual escapes can then proceed in rapid succession with but a few seconds interval between departures. The techniques is simple and requires but little effort. All personnel know what is going on at all times. If a man happens to "freeze" in the trunk he can immediately either be forcibly ejected or drawn back into the compartment. This procedure would have eliminated the long delays between successive escape parties which were so disastrous for Tang and it is quite possible that more men would have been forced to make the escape attempt and therefore more would have reached the surface alive.
22-15. The principal disadvantages of the skirted trunk for escape at great depths are as follows:
(a) During and after the period of flooding the escape compartment to equalize internal pressure with the sea, personnel within will be subject to nitrogen narcosis, CO2 poisoning, and the deleterious effects of other noxious or toxic gases which may be present, such as chlorine, carbon monoxide, smoke, etc., since these gaseous components will be under higher than normal pressures. For example, the concentration of CO2 content by volume, which would be harmless at atmospheric
pressure will have about the same physiological effect as thirty per cent CO2 content by volume at atmospheric pressure and will cause death in a very short period of time. Approximately the same holds true for nitrogen and noxious or toxic gases. At pressures corresponding to depths greater than 150 feet, this effect may become so pronounced that personnel can remain conscious only for very limited periods of time, particularly if the atmospheric initially contains smoke, toxic gases or higher than normal portions of CO2. Increasing the percentage of oxygen in the air may also introduce the possibility of oxygen poisoning at high pressures.
(b) Breathing air at high pressure will render an escaping man susceptible to air embolism and caisson disease ("bends), particularly if ascent is rapid as in the "free" escape method. At 300 foot depth, for example, a man could not safely make a "free" ascent after breathing air at the equivalent pressure for more than about three minutes, and for an even shorter time if he has already been subjected to a flooding period during which air pressure was raised gradually.
(c) Unavoidable immersion of personnel in cold water during the flooding period may cause deaths by drowning or exposure prior to the escape attempt.
These factors are considered to render the skirted-type trunk useless for escape at depths much below 150 feet for the average person, although from a standpoint of simplicity there is much to be said in its favor. The principal and very great advantage of the air-lock type escape trunk is that it enables rapid compression of the escape party to sea pressure and permits remaining personnel within the ship to stay at pressure near normal while awaiting their turn.
22-16. In considering problems involved in the successful execution of individual escapes, the debilitating effect on mind and body of some or all of the following possible conditions must constantly be borne in mind:
(a) The shock effect on personnel of the initial accident or damage which caused the sinking.
(b) The presence of seriously injured or mentally deranged personnel.
(c) Lack of lighting.
(d) Exposure to heat or cold and excessive humidity.
(e) Continued breathing of poor or toxic atmosphere.
(f) Excessive trim or list on the submarine which may render even normal movements difficult.
22-17. It is clearly evident in the light of available experience that the first requirement of any escape method is that it be simple and so calculated as to obtain the highest percentage of survivors. It is also apparent that present methods are not satisfactory at deep depths.
22-18. The British are currently investigating the use of a small cylindrical one-man escape chamber fitted with hatches top and bottom and provided with a mechanical apparatus permitting forced ejection of a man from within the trunk if necessary. This trunk would be intended for use in conjunction with both "free" and "lung" escapes. The system is believed by the British to have the following advantages:
(b) The escaping man has no control over the operation once he enters the tank, and whether dead, unconscious or confused, he can be forcibly ejected to make room for the next man.
(c) A total trunk operation cycle time of about 4 or 5 minutes appears possible.
(d) Brief subjection to air at high pressure minimizes the chance of nitrogen narcosis, CO2 poisoning, air embolism and caisson disease.
22-19. In this country, as stated previously, further research and development studies are underway by the Navy Department in an effort to improve submarine search and rescue equipment. One line of investigation which may prove of great value is the use of helium-oxygen mixtures in conjunction with a breathing device and which possibly may permit use of the skirted-type trunk for escape at all depths up to the collapse depth of the submarine itself. The "flooding up" stage, which is a necessary preliminary to a skirted-trunk escape, is particularly critical due to the inability of average individuals to remain conscious for even short periods when breathing a normally proportioned air mixture at high pressure. For example, it is considered likely that if an escape compartment were slowly flooded at a depth of 350 feet, most normal personnel within would be incapacitated or unconscious before internal pressure had been equalized with sea pressure. It has been determined that the air component chiefly responsible for unconsciousness when breathing under high pressure is the nitrogen portion. When the nitrogen is replaced by helium, unconsciousness does not occur at least up to 500 feet and there is reason to believe that unconsciousness will not occur at depths considerably greater than 500 feet inasmuch as the intoxication preceding coma does not occur to any extent even at 500 feet when using helium. From a physiological point of view, the "lung" itself is believed to be capable of permitting safe ascent from depths considerably greater than 500 feet, providing the proper breathing mixtures can be continuously provided and decompression rules are carried out.12 Divers using helium-oxygen mixtures, for example, have worked
at a depth of 440 feet in conventional diving suits.13 Initial inflation of "lungs" with helium-oxygen mixtures would also facilitate and may even be mandatory for air-lock escapes at extreme depths. The depth limitation of the present "lung" for individual escape, using oxygen alone, is considered to be about 200 feet for normal men, and it is believed that helium-oxygen mixtures should be used at all depths greater than 200 feet.14
22-20. Other projects which are currently being investigated and which may prove of practical value for locating sunken submarines and for escape therefrom are:
(a) Development of a radio beacon which can be ejected from a signal ejector on a sunken submarine to give automatic distress warning signals useful for homing by searching vessels.
(b) Development of a noise source, such as a sonar test target with increased power, suitable for sonar homing.
(c) Dye markers which can be ejected from a signal ejector to indicate location.
(d) Development of a short range emergency-power underwater sonar telephone system which can be used for communications during rescue operations.
(e) Development of a messenger buoy and modification of present rescue chambers for operations at great depths, as mentioned in paragraph 22-9.
(f) Modification of the "lung" to provide a collar for buoyant support of the head after reaching the surface (similar to German apparatus), in order to lessen the chance of drowning if the wearer becomes unconscious after surfacing.
(g) Provision of equipment for mooring submarine rescue vessels in 850 feet of water.
(h) Development of a simple battery-powered two-way voice communication system between the escape trunk and compartment below. The experiences of Tang (SS306) and Sirago (SS485) demonstrated the inadequacy of attempting communications by hammer taps or other such means.
(i) Experimental investigations in "free" escape techniques.
Table of Contents
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1. See Tang narrative, Section X.
2. U-3, 18 January 1911; USS O-5, 29 October 1923; HDMS Dykkeren 10 October 1916.
3. USS Squalus, 23 May 1939.
4. HMS K-13, 29 January 1917.
5. HMS Thetis, 1 June 1939, 95 men; U-51, World War I, 16 men; U-741, World War II, number unknown.
6. HMS Untamed, 30 May 1943, 36 men.
7. UB-57 World War I, number unknown; HMS Strategen, November 1944, possibly 4 men.
8. U-767, World War II, 6 men.
9. U-859, World War II, 4 men.
10. HMS Thetis, 1 June 1939, 4 men.
11. Four 7-man CO2 inflated life rafts will be furnished to each active submarine as soon as available and the hull allowance lists have been modified accordingly. Sea Fox (SS402) conducted tests which demonstrated the practicability of ejecting such rafts from torpedo tubes, using torpedo impulse air. It is expected that deaths due to exposure and drowning subsequent to reaching the surface should be reduced by successful use of these rafts in conjunction with escape operations.
12. "Lungs" have been used with normal air mixtures at simulated depths as high as 354 feet in the mine tank of the U.S. Naval Gun Factory, Washington, D.C. Actual escapes were made in the open sea off Key West, Florida, at depths up to 200 feet from the torpedo room and motor room of S-4 (BuC&R ltr. No. L9/P-(14) (ME)N/C; EN7/A2-11 of 10 September 1929).
13. U.S. Navy divers reached 440 foot depth without suffering adverse effects while inspecting O-9, lost with all hands on 20 June 1941 off the Isles of Shoals. A 90/10 helium-oxygen mixture was used.
14. Helium-oxygen mixtures can be quite easily provided for submarine bow and stern compartments in a manner similar to that now used for oxygen stowage.