Section XIX
Engineering Notes

19-1. When it is considered that the propulsion plant of a modern U.S. submarine, including the batteries, occupies about one-half the length and over one-third the volume of the hull, it is certainly remarkable that the incidence of serious damage to such equipment due to war action was extremely low. In only one known instance, Grenadier's (SS210) action of 22 April 1943, was a propulsion plant completely and permanently disabled, and in only one other known case, Perch's (SS176) action of 2 March 1942, was a propulsion plant damaged so heavily as to be a significant factor in the eventual loss of the vessel. However, propulsion power submerged was temporarily disrupted on our submarines in over fifteen separate occasions as the result of underwater explosive attacks, and with serious consequences in a few instances. All of these temporary power disruptions were caused by failure of electrical equipment, principally through tripping of relays and contactors due to shock or jarring together of energized control cubicle busses. They occurred for the most part early in the war on older ships where shock protection measures had not yet been carried out. That serious damage did not occur more frequently to U.S. submarine propulsion plants was due principally to the following: (1) the inherent ruggedness of the propulsion motors, generators, batteries, reduction gears, Diesels, shafting and propellers; (2) the improvements made in the shock design and shockmounting of vulnerable equipment, particularly the introduction of laminated main storage battery cells, shock-proof relays, shockmounted propulsion control cubicles and fitted foundation bolts to prevent misalignment of the propulsion motors and reduction gears; and (3) effective casualty control through split plant operation.

19-2. Although many casualties were sustained by U.S. submarine propulsion and auxiliary Diesel engines in the course of normal service, there are only a very few instances in which these engines are known to have sustained damage as the result of war action. War experience has conclusively demonstrated that modern U.S. submarine Diesel engines, both propulsion and auxiliary, regardless of make, are practically impervious to damage of disabling nature, even at those explosive ranges which will cause near destruction of the pressure hull. The experiences of Kingfish (SS234), Salmon (SS182), Scamp (SS277), and Halibut (SS232) are excellent examples since all four of these vessels sustained permanent pressure hull deformation in way of the machinery spaces.2 No damage at all was received by the Diesels on Kingfish and Halibut. On Scamp, No. 2 propulsion engine (FM Model 39-D-8-1/8) was disabled when the pressure hull bulged sufficiently to come hard up against the scavenging blower of that engine (Photo 9-11). Scamp's other engines remained completely operable, however. On Salmon, all engines


(GM Model 16-278A) either partially or completely flooded through leaking exhaust lines, but none were physically damaged by the attack. However, the drive shaft of the scavenging blower for No. 1 propulsion engine subsequently fractured when an attempt was made to start the engine before dewatering had been completed. Salmon's other three engines operated satisfactorily. On Grenadier, in the action leading to her loss on 22 April 1943, the propulsion Diesels apparently remained operable after the bomb attack although severe hull damage was sustained in way of the machinery spaces, for it was reported that smoke was cleared from the interior of the boat, after surfacing, by running the engines. On Perch, two engines remained operable after the first series of depth charge attacks but only one engine could be run after the second series of attacks. One engine limited her surface speed to about five knots. One of the three damaged engine (Winton Model 16-201A) was disabled by a broken camshaft. The cause of failure of the other two engines was not reported. The auxiliary Diesels were not damaged.

19-3. The most frequent casualties which occurred to Diesel engines incident to close underwater explosive attacks were the following: engines flooded through leaking exhaust valves;3 lube oil, fuel oil and circulating water lines ruptured or developed leaks, usually minor; engine foundation bolts sheared; and engine thermometers and other gages were broken or deranged. Such casualties are of minor nature, in no case have disabled an engine for more than a temporary period, and are not peculiar to war damage since similar casualties have occasionally resulted during normal service operations, due to leaking exhaust valves or excessive engine vibration. That our submarine Diesels have withstood close attacks with but minor or no damage occurring is attributable to the following reasons: (1) the rugged welded steel construction of the engine frames, resulting in high energy absorption characteristics, (2) the rugged construction of the engine components, and (3) the large mass of the engines. Assuming both to be directly mounted, the relative shock strength of a heavy item of equipment, such as a propulsion Diesel engine, need not be as great as the strength of a small and light item, as for example, a relay or an instrument. This is because a large, heavy item has a weight comparable in magnitude to the weight of the ship's hull and the foundation in the immediate vicinity of the equipment, and consequently the large mass and rigidity of the engine and its structural foundation modify the shock motion of the hull locally. Moreover, the rigidity of a Diesel engine is comparable to or may exceed that of the foundation and hull, so that for severe shock motions the hull and foundation will tend to absorb a relatively large percentage of the shock displacement, whereas the engine will remain almost stationary. In the case of a heavy machine, the forces that can be transmitted to the machine by shock may be limited by the strength of the foundation.

19-4. The propulsion motors and generators have also been singularly free from war damage casualties and for reasons similar to those


enumerated above for the Diesel engines. There is no known case where propulsion motors or generators have been disabled on U.S. submarines through direct war damage to the motors or generators themselves, regardless of their type and make. In one case, Sailfish's (SS192) action of 7 December 1943,4 a propulsion motor arced to ground and sustained brush rigging damage which disabled it until repairs were accomplished by ship's force, but this casualty was caused by failure of control equipment in the cubicle rather than direct damage to the motor itself. There are a few instances where brush rigging on propulsion motors has been slightly deranged or has jarred slightly out of position but the effects have been minor in all such cases. Reports have also been received where brush rigging on propulsion motors has been dislodged through shearing of rivets, or where brushes have overheated or chattered, and these casualties have been attributed to close depth charge or bomb attacks. However, it is believed that most of the latter cases were due to improper securing of the brush pigtails since such casualties also resulted from normal service operations. Corrective steps were taken in the manufacture of these brushes in 1944 and, so far as is known, no further brush difficulties were encountered thereafter. No reports have been received by the Bureau of any war damage having occurred to main generators. This is partly attributable to the fact that the generators are not energized during submerged operations and therefore derangements of control equipment will not cause minor damage to the generators, as has occurred in a few cases to propulsion motors.

19-5. The only component of submarine propulsion plants which war experience demonstrated to be particularly vulnerable to damage and which frequently caused loss of propulsion, was the propulsion electrical power and control gear, principally the equipment contained in the propulsion control cubicle. Of the fifteen cases known to the Bureau where propulsion failed temporarily on submarines while submerged and undergoing attack, all were due to electrical casualties. These casualties can be divided into three general types: (1) tripping of propulsion overload relays due to shock (later replaced by shockproof overload relays), (2) operation of relays due to momentary movement and short-circuiting of energized bus bars in the control cubicle and (3) control cubicle electrical fires caused by short-circuiting of energized circuits. The urgent need for improving the shock resistance of submarine propulsion electrical control equipment was demonstrated by the controlled depth charge tests conducted with Tambor (SS198) and Trout (SS202) early in 1941, before our entry into the war. Two principal corrective measures were proposed: (1) improving the shock resistance of the separate components, such as switches, contactors and relays, and (2) the shockmounting of the entire propulsion control cubicle to reduce the acceleration forces on vital equipment contained in that enclosure. Following the tests on Tambor and Trout, the submarine Gar (SS206) was provided with the first experimental installation of a shockmounted propulsion control cubicle, designed and constructed by the General Electric Company and employing


rubber pads as the resilient material for shock reduction. Several experimental overload relays were also installed in Gar to test the relative merit of various designs. Controlled explosion tests were then conducted which demonstrated that shockmounting of the entire control cubicle was a practicable method of reducing damage to the vital electrical control gear and that the designs of switches, contactors, and relays could be so improved as to provide a high degree of inherent shock protection. The Bureau therefore authorized the shockmounting of propulsion control cubicles on both submarines in service and new construction.5 In addition, overload relays in the main battery power and propulsion motor and generator circuits were replaced with shockproof types and, on applicable submarines, lock-out cams were installed to prevent maloperation of the series and parallel contactors in the main control cubicle.6 As a result of Tunny's (SS282) experience of 26 August 1943, where propulsion power was disrupted temporarily due to a fire which started when the positive and negative main battery busses in the control cubicle jarred together momentarily, the installation of small phenolic bumpers between the cubicle main battery busses was authorized for all applicable submarines to prevent recurrence of similar casualties.7

19-6. The effectiveness of the shock protection afforded by the above alterations can best be judged by the fact that so far as is known with only four exceptions, all cases of loss of propulsion power traceable to derangement or maloperation of electrical equipment occurred prior to 1944 and on vessels which were not provided with shockproof relays and/or shockmounted control cubicles. The four exceptions were as follows:8 (1) Tunny's action of 30 March 1044 in which energized bus bars short-circuited by movement against the control cubicle frame. This damage is believed traceable to the fact that, although the cubicle had been shockmounted, the shock protection afforded by the resilient mounts was reported to have been nullified by one support frame which was improperly mounted so that it made direct metallic contact with the cubicle cage. (2) Picuda's (SS382) action of 20 May 1944 in which a close depth charge detonation tripped the starboard propulsion motor contactor in the control cubicle. The contactor was immediately closed, however, and propulsion was restored. (3) Sandlance's (SS381) action of 7 August 1944 in which the starboard propulsion control cubicle controllers were jammed by a broken washer and limited the maximum speed on the starboard shaft to two-thirds until repairs were made. (4) Cobia's (SS245) acton of 14 May 1945 in which the battery and generator busses in the control cubicle arced, causing flame and smoke and the welding together of the contactors. Power was secured and the ship went to the bottom.


19-7. The importance of insuring that foreign objects and inadequately attached fittings are removed from areas over or adjacent to propulsion control cubicle has been illustrated by several experiences where propulsion power was lost and/or fires were started due to short-circuiting of energized power circuits by small objects falling from the overhead or being hurled into the cubicle from the sides. Scamp's action of 7 April 1944 (Section IX) is such an example.

19-8. The presently accepted standard U.S. submarine main storage battery jars are of laminated construction having a hard rubber exterior and a soft rubber inner layer. War experience has demonstrated that battery jars of this type are highly resistant to shock and can be considered generally satisfactory for war service. The introduction of laminated battery jars together with improvements in the design and support of the battery tanks are major factors in the resistance of submarines to damage. The lining of the battery tanks with rubber also probably contributes to the shock-proofness of the batteries. Submarines which have sustained close attacks, but where no pressure hull deformation occurred in the vicinity of the battery tanks proper, have in all cases either had no battery jar damage at all or the jars have cracked on only a very small number of cells. It is also significant to note that in the majority of those cases where jars were reported as having cracked, no loss of electrolyte occurred since only the outer hard rubber exteriors of the jars cracked and the inner soft rubber portions remained intact. Even where jars have lost electrolyte and caused short-circuiting, no serious consequences have resulted since the damaged jars were easily disconnected. In only two instances have relatively large numbers of battery jars been damaged on U.S. submarines which survived close attacks; on Halibut (SS232), 14 November 1944; and on Redfish (SS395), 10 December 1944. In both of these cases the battery jars were of laminated construction. On Halibut, the hull forward of frame 55 was extensively damaged and the pressure hull plating in way of the forward battery well was dished in by as much as from one to two inches. About seventy percent of the 126 jars in the forward battery developed cracks through their outer hard rubber casings (Photo 19-1). On all but eleven jars, the soft rubber inerts were undamaged and no leakage of electrolyte occurred. On the eleven jars which lost electrolyte, the leakage occurred through cracks in the jar bottoms. The fact that only eleven jars actually leaked, although a total of about eighty jars had cracks in their outer casings, is convincing evidence of the value of the laminated soft rubber insert construction. No damage was reported to have occurred to the after battery jars. On Redfish, the forward portion of the pressure hull was also considerably deformed although no dishing was reported in way of the forward battery well itself. Twelve jars of the forward battery were cracked and lost electrolyte. No damage was sustained by the jars of the after battery. In neither of the above two cases did the damage to the batteries have serious effect on ship operation. When the extensive pressure hull damage which occurred close to the battery wells on both Halibut and Redfish is compared with the battery damage on those two vessels, it appears that current submarine battery cells and their method of installation approach the shock resistance to the hull itself.


19-9. In numerous instances, full battery grounds have developed as a result of close attacks. In most cases these have been traceable to short-circuits in the emergency lighting systems or short-circuiting of one or more cells caused by electrolyte spillage through cracks which developed in the battery cell top sealing compound and thence establishing leakage paths to uninsulated tie-rods and strongbacks connected to hull structure. Cracks occurred in the sealing compound due to shock but in many cases this tendency was aggravated by improper wedging or faulty tightening of strongbacks. To eliminate casualties due to acid spillage through cracked sealing compound, two steps were taken: (1) all tie-rods and strongbacks in the battery wells were insulated with a rubber compound, and 2) improved sealing compounds were developed. To facilitate locating the cause of battery grounds, switches were installed in the emergency lighting circuits on all fleet type submarines to permit separation of emergency lighting from the battery for battery ground readings.9

19-10. War experience has repeatedly demonstrated that reduction gear drive propulsion plants are unsuitable for modern submarine warfare in that the main reduction gears are extremely susceptible to tooth damage when subject to underwater explosions at even moderate ranges. Tooth damage causes high noise level, usually described as "clicks", "thumps", or "knocks", which reduces or invalidates the military effectiveness of submarines since approach and evasion tactics then become hazardous or impossible when enemy vessels are equipped with sonar listening gear. In approximately eighteen instances, U.S. submarines have reported that excessive reduction gear noise developed as the result of enemy depth charge or bomb attack. In at least three actions, reduction gear damage forced early termination of patrols and the subsequent repairs to achieve quiet operation were long and expensive.10 Reduction gear damage has in no case prevented the gears from operating mechanically but has been objectionable from the standpoint of the introduction of high noise level. Tooth damage has apparently resulted either from sudden and violent movements of the pinion and bull gear masses relative to each other or in some cases perhaps from longitudinal movement of the entire propeller shafting. For example, a clicking noise developed in the reduction gears of Apogon (SS308) when forward area repair forces removed a damaged propeller on that ship, without drydocking, by detonating small explosive charges on the forward blade faces. Since the shaft coupling in the motor room was not broken, the shaft tended to move aft as a whole and caused sudden relative movement of meshing tooth surfaces in the reduction gear. A similar action could probably occur on a submarine when subjected to close underwater explosive attack. In addition, the continuous reduction in self-generated noise accomplished by design improvement of components and by sound isolation measures resulted in the noise caused by reduction gears, even though undamaged, to become a prominent noise feature, whereas in earlier fleet submarines, the reduction


gear noise was not as high a that of other items. This, together with the war experience in regard to damage, led the Bureau to change from reduction gear drive for submarines to direct drive. The move, which required considerably more weight for the low speed direct drive motors, was made possible by weight savings that had been realized through careful design of various components and by the elimination of unnecessary ones.

19-11. Main engine air induction and ship's supply ventilation hull flapper valve discs and/or their seats have in several instances been deformed by close explosive attack. When the induction line itself concurrently flooded, as sometimes occurred, sea water then entered the machinery spaces, occasionally in considerable volume. Early in the war, leakage which developed around these hull flapper valves was in several instances successfully stopped or reduced to a minor quantity by forcing the valve flapper against its seat with the aid of a chain fall as on Kingfish during her action of 23 March 1943 (paragraph 5-21, Photo 5-8). In July of 1943, gagging dogs were authorized for installation in engine air induction and ship's ventilation hull valves on those submarines not previously provided with emergency means of securing such valves.11 It should be noted that leakage through induction valves will always accumulate in after compartments and therefore may cause a submarine to become heavy aft, flooding of the topside induction piping also contributing to this tendency. The majority of instances where U.S. submarines have lost depth control due to flooding have been the result of added weight aft through induction hull valve leakage. The introduction of welded joints for the induction piping topside, commencing early in 1944, practically eliminated cases of flooding of such piping and therefore the prospect of flooding into the interior of the hull through distorted induction hull valves has been reduced markedly. Projected submarine designs will incorporate a snorkel type air intake and consideration will be given to running the induction piping system leading from the snorkel intake to the machinery spaces entirely within the confines of the pressure hull. The number of large openings in the hull for air purposes would thereby be reduced to only that at the snorkel itself.

19-12. Wiring passing through the pressure hull to external instruments or fittings exposed to full sea pressure has proved to be quite vulnerable to damage unless special precautions are taken. The failures encountered have been of two general types" (1) leakage through cable sheathing causing direct shorting of the cable conductors or allowing water to reach terminal boxes, switchboards, or equipment, and (2) leakage around pressure hull stuffing boxes. As an example of the former, the experience of Sculpin (SS191), on her second patrol is interesting. On 7 February 1942, while undergoing depth charge attack at a depth of 345 feet, the multiple conductor cable to the port annunciator flooded through the annunciator box on the bridge. Water than passed


through the length of the cable to the IC board in the control room, started a small fire, grounded numerous circuits, and ultimately placed the entire torpedo firing circuit and battle order transmitter and indicator systems out of commission. There are many cases on record where cables passing through the pressure hull have been forced inward through their stuffing tubes during close attacks, some by as much as one or two feet. In such cases, leakage has usually occurred at the stuffing tubes. Several corrective measures were taken to eliminate such casualties. Following a method developed by the Naval Shipyard, Portsmouth, rubber stop rings were vulcanized directly to cable sheathing at the outboard sides of all pressure hull stuffing tubes, using special molds for each size of cable, to prevent cables from being forced in.12 Cable ends external to the pressure hull were terminated with vulcanized seals to prevent water entering the sheathing. Similar methods were developed for packing terminal tubes and sealing cable ends for cables entering pressure proof fixtures. On older vessels, external cables no longer required for ship operation were removed and the hull stuffing tubes blanked. Cables leading from conning tower equipment to the main pressure hull, which formerly were routed outside the hull and therefore exposed to full sea pressure, were rerouted through a specially enlarged conning tower hatch trunk so as to be entirely within the pressure hull,13 and an additional cable trunk was authorized for installation between the conning tower and control room to accommodate the additional cable required for SJ radar and other new equipment. Casualties to external cables were practically eliminated in those vessels on which the above alterations were accomplished. In those few cases where cable sheathing leaks did occur subsequent to the above alterations, it is believed that the cause of leakage can be traced to improper cable end sealing.

19-13. On 17 August 1942, a serious fire occurred in the after battery tank of Bass (SS164) while operating off Balboa, C.Z., on her fourth war patrol. The fire was believed to have been caused by a short circuit resulting from leakage paths across phenolic insulation. Twenty-six members of the crew in after compartments, most of whom were asleep when the fire started, were trapped and died either through asphyxia or from the toxic effects of the fumes generated by burning phenolic material. In order to eliminate the possibility of similar casualties on other submarines, instructions were issued to remove phenolic material from certain places in submarine battery tanks.14 On 7 April 1944, another serious casualty resulted from burning phenolic material, this time on Scamp (SS277), and very nearly caused the loss of the vessel.15 On that ship, large quantities of toxic phenolic smoke were generated by a very small electrical fire at a phenolic-insulated rotary switch in the control cubicle. The Bureau was long aware of the undesirable properties of phenolic resins for shipboard insulation use and during the war years many research and development contracts were let with industry with


the view of obtaining a more satisfactory material. By early 1944, a new organic insulation material made of melamine resin rather that phenolic resin had been accepted. Tests demonstrated that the insulation and shock properties of melamine were equal to or greater than those of phenolic but that melamine would not support combustion. Phenolic material, once ignited, will continue to burn and will generate large quantities of toxic fumes, whereas the combustion of melamine will result in only 40 percent toxic gases as compared with phenolic material, will only decompose when actually subjected to high temperature, as from an electric arc caused by short-circuiting, and all combustion will immediately stop when the source of heat is removed. It is possible on Scamp, for example, that the volume of toxic gases given off by the burning phenolic material was very much greater than the volume of gases which would have been generated had melamine material been installed. By May of 1944, melamine production had reached a sufficient volume so that its use as an insulation material combined in laminated construction with glass cloth was authorized for submarines, the first installations being made in the split-type control cubicle on direct drive submarines then under construction. The introduction of melamine insulation for submarine electrical equipment is considered to have greatly reduced the hazard from toxic gases originating from electrical fires and constitutes an important peacetime safeguard as well as a wartime necessity.


Photo 19-1: HALIBUT (SS232). View showing cracks in hard rubber outer casing of laminated battery jars
Photo 19-1: Halibut (SS232). View showing cracks in hard rubber outer casing of laminated battery jars on Halibut (SS232) as a result of her action of 14 November 1944. Although about 80 jars of the forward battery developed cracks in their outer casing, only 11 jars lost electrolyte.


Table of Contents
Previous Section (XVIII) * Next Section (XX)


1. Grenadier narrative, Section VIII and Perch narrative, Section IV.

2. Kingfish, Section V; Salmon, Section VII; Scamp, Section IX; Halibut, Appendix I.

3. Salmon, Section VII; and Permit, 13 February 1944, Appendix I.

4. See Appendix I for brief of Sailfish damage.

5. Authorized for new construction by BUSHIPS ltr. SS212-284/S41 (3660) of 11 December 1941 and for ships in service by ShipAlt SS131 of 7 August 1942 (delay for ships in service was due to priority assignment of materials and design work for ships being constructed).

6. ShipAlt SS218 of 17 November 1943.

7. ShipAlt SS222 of 6 November 1943.

8. Briefs of damage sustained by each of these four ships are contained in Appendix I.

9. ShipAlt SS224 of 21 December 1943.

10. Sand Lance (SS381), 7 August 1944; Barbero (SS317), 27 December 1944; and Bergall (SS320), 13 June 1945. See Appendix I and Section XIV for details on damage.

11. ShipAlt SS201 of 7 July 1943.

12. Authorized by BuShips ltr. SS/S62-2(660u-815); EN28/A2-11 of 31 March 1944.

13. Authorized by BuShips conf. ltr. SS/S62-2(515) of 2 March 1944.

14. BuShips ltr. SS/S39-1(8660-3660); EN28/A2-11 of 10 October 1942.

15. See Scamp narrative, Section IX.

Transcribed and formatted for HTML by Patrick Clancey, HyperWar Foundation