Naval rearmament, which began in the mid 1930s, and WWII had dramatic impact on U.S. torpedo programs. Three of the most significant changes were the enormously increased requirement for torpedoes, the urgent need for new torpedo types and the first use of U.S. torpedoes against enemy vessels. The increased requirement was satisfied by expanding government facilities, the Newport Torpedo Station (NTS-Newport) was enlarged, the Alexandria Torpedo Station was reopened’ and Keyport Torpedo Station began assembling torpedoes, and by initiating civilian production. Total production between 1939 and 1945, almost 60,000 torpedoes, was about equally divided between the torpedo stations and contractors. Mk 14 torpedoes were, however, in such short supply in 1942 that some fleet boats loaded out with Mk 10 torpedoes or even Mk 15s in the after tubes.2 New types of torpedoes are discussed in Part Three of this series. Firing war shots was an almost totally new experience for the U.S. Navy. It seems probable that the number of warbots fired against enemy vessels in December 1941 was larger than the total number of warbots torpedoes fired for any purpose’-in the entire past history of the U.S. Navy. Perhaps not surprisingly, this intensive use of torpedoes revealed shortcomings that had been previously obscured, especially in the new service torpedoes and particularly in the Mk 14.
The trio of new service torpedoes, Mk 13, Mk 14 and Mk 15, which represented the bulk of the U.S. Navy torpedo development in the 1930s were on the one hand excellent weapons and bad long service lives-the Mk 13 remained in service until 1950, the Mk 14 was a valuable service weapon until 1980 and Mk 15 served as long as 21 inch torpedoes remained on destroyers. On the other hand they all had significant problems that were only fixed after wartime use began. The Mk 14, which was the principal submarine weapon, was plagued with defects that vitiated its use as a weapon until mid 1943. The conflict between the shore establishment and the operating forces over these problems was a very significant and much discussed factor in U.S. submarine operations during WWII.
The Great Torpedo Scandal
The Great Torpedo Scandal” emerged and peaked between December 1941 and August 1943, but some of its roots went back 25 years. It involved primarily the Mk 145 and three distinct problems, depth control, the magnetic influence exploder and the contact exploder, whose effects collectively eroded the performance of the torpedoes. The scandal was not that there were problems in what was then a relatively new weapon, but rather the refusal by the ordnance establishment to verify the problems quickly and make appropriate alterations. The fact that after 25 years of service the Mk 10 had newly discovered depth control problems adds weight to the characterization of the collection of problems and responses as a scandal. These comments should, however, be mitigated a little by the fact that each of the Mk 14 problems obscured the next. Although Buord did not identify the final problem, contact exploder malfunction when a torpedo running at high speed struck the target at 90 degrees, their response, once the difficulty bad been identified, was notably prompt. It spite of the promptness of Buord’s response, by the time it reached Pearl Harbor a number of relatively simple solutions to the problem bad been proposed, and modifications bad already been designed and implemented. This was, however, almost two years after the United States entered WWD.
Torpedo Depth Control
The first of the U.S. torpedo problems was deep running which was a frequent torpedo problem in various navies beginning at least as early as WWI. The problem, however, was not always
due to the same sort of defect. 7 There are at least four distinct kinds of problems that impact depth control:
1. Differences between calibration shots and service/warshots
a. Torpedo weight or balance changed in converting to warshots, for example, warheads that were heavier than calibration heads.
b. Calibration firings failed to simulate service launch conditions, for example, calibration firings from barges or surface vessels rather than submerged torpedo tubes, and/or calibration shot launch speeds, i.e., the speed at which the torpedo leaves the tube, and accelerations during launch different from service conditions.
2. Design or manufacturing defects causing changes in calibration after proofing or effectively causing calibration to change with time or environment, for example, sensing water pressure where flow corrections were large, or depth spring fatigue, or leaky castings, etc.
3. Erroneous calibration: failure to check against an absolute standard, for example, total reliance on hydrostatic depth measurement and failure to use nets, soft targets or other sensing systems to establish true depth.
4. Inadequate understanding of the technology involved, for example, failure to recognize the importance of hydrodynamic flow in sensing the pressure at the skin of a fast torpedo; lack of understanding of the feedback loop and depth control dynamics.
Amazingly, U.S. torpedoes, especially the Mk 14, demonstrated that most of these possibilities could, in fact, occur.
Depth control problems with U.S. torpedoes were suspected by NTS-Newport and Buord even before the United States entered WWII. On 5 January 1942 Buord, based OD earlier (1941) testing, advised that the Mk 10 torpedo, which had entered service in 1915, and was still used in S class submarines, ran four feet deeper than set.’1 NTS-Newport tests on the Mk 14 torpedo in October 1941 had been interpreted as indication that it too ran four feet deeper than set, but this was not reported to the submarine commands at that time. War patrol experience led to fleet suspicions that the torpedoes ran deep and these thoughts were communicated to Buord. In response to a direct order from the Chief of the Bureau of Ordnance, additional NTS-Newport tests in February-March 1942 Confirmed four foot error for the Mk 14. Rear Admiral William H. Blandy, Chief of Buord, notified Rear Admiral Thomas Withers, Jr., COMSUBPAC, of the problem in a letter dated 30 March 1942, but general notification to the submarine forces was not made until Buord issued Buord Circular Letter T-174 dated 29 April 1942. The language in correspondence between Withers and Blandy indicate that Newport and Buord believed that the four foot error in Mk 14 depth was due to calibrating torpedoes with test heads that were lighter than the warhead. This would cause torpedoes with warheads to run deep both because of increased weight and a most heavy trim. The Mk 14 depth control problem was, however, much more severe than the four feet acknowledged by NTS-Newport.
In a mood of desperation, the operating forces made their own depth determinations, using fishnets for depth measurement, at Frenchman’s Bay in Australia on 20 June 1942. These measurements indicated that the depth errors were probably more like 11 feet.’° Buord and NTS-Newport criticized the methodology and were reluctant to accept the results of the Frenchman’s Bay firings and it was not until August of 1942, after intervention by the CNO, Admiral Ernest J. King, that they re-investigated and agreed that there was a 10 foot depth error in the Mk 14 system. Interim instructions for fixing the problem were issued very quickly and kits to effect an official alteration were distributed in late 1942. As near as we have been able to determine, there were two independent problems: trim change due to warheads heavier than calibration heads and sensing the water pressure at a point where the velocity head was significant and consequently the measured pressure was low. The fix for the latter moved the pressure sensing port to the interior of the free-flooding midbody where the pressure was close to the true hydrostatic pressure and so reflected the true depth. The modified torpedoes were identified by the suffix A added to the Mod with the most famous being Mk 14 Mod 3A.
Since the hydrodynamic problem has seldom been explained in readily accessible documents, we give a brief summary here. The pressure along the length of a torpedo varies because the velocity of the water relative to the surface varies. The pressure at the nose is higher than the hydrostatic pressure, which is proportional to depth, by an amount proportional to the square of the torpedoes speed. This corresponds to a depth of 39 feet of seawater for a torpedo moving at 30 knots or 88 feet for a 45 knot speed. As the measuring point is moved back along the skin of the torpedo the pressure decreases rapidly and becomes substantially less than the hydrostatic pressure. The pressure subsequently rises but remains slightly less than the hydrostatic pressure along most of the cylindrical section. Finally along the conical afterbody the pressure again drops and then rises though, since the actual flow is not streamline, not to the values found at the nose. The critical point is that the pressure at the skin of a torpedo is generally different from the hydrostatic pressure corresponding to the torpedo’s depth. The deviation is substantial in the nose and tail cone regions. A depth error due to the measurement of the wrong pressure would, of course, be detected in any calibration process that used an absolute depth measurement for reference. Unfortunately the Torpedo Station used a depth and roll record which determined depth by measuring the water pressure and was thus subject to the same kind of error as the depth gear. Furthermore, the depth and roll recorder was placed in the test bead at a point where the hydrodynamic pressure was less than the hydrostatic pressure by almost the same amount as at the location, in the afterbody. of the sensing port for the depth gear. Thus both the recorder and the depth gear sensed essentially the same pressure, though not the hydrostatic pressure, and the torpedo appeared to be running at the set depth. The depth engine, however, responded to the lower pressure by adjusting the horizontal rudders to correct this error and the torpedo ran deep. The hydrodynamic theory needed to understand this problem was readily available in the 1930s but most design engineers were quite probably not acquainted with it. In consequence, it was assumed that since the depth recorder showed the correct depth, the torpedo was running at the correct depth. There are other insidious aspects to this problem. One of these is that a depth recorder checked against depth by static immersion in water to various depths or in a pressurized tank of water reads correctly since the error described above is due to hydrodynamic flow. Further the error is proportional to the square of the torpedo speed and is thus almost twice as important for a 46 knot torpedo as it is for a 33 knot torpedo. None of these comments, however, justify or excuse the failure to use an absolute standard to verify the results obtained with the depth and roll recorder or the obdurate resistance to complaints from the operating forces.
The operational aspects of the depth control problem have been recounted many times. 11 The Mk 10 problem, which was probably dominated by the error caused by the change from exercise heads to warheads, was handled by simply setting the torpedo to run at a shallower depth and this procedure was implemented in January 1942, over 2S years after the weapon entered service. The Mk 14 problem required both a calibration modification and a modification to sense water pressure in the midships section and the latter was implemented beginning in the last half of 1943.
The Magnetic lnfluence Exploder
The second problem with the Mk 14 torpedo was the erratic performance of the magnetic influence feature of the Mt 6 explored. Magnetic influence explodes had great appeal as proximity fuzes for torpedoes offering the possibility of detonating the warheads under the vulnerable bottoms of warships. This potential advantage led most of the major navies to attempt to develop such explorer and generally these first attempts were not successful in service use.
The basic idea of a magnetic influence exploder is to sense either the field due to permanent magnetization of a ship’s hull or the perturbation of the earth’s magnetic field caused by the large quantity of relatively high permeability ferrous metal in the ship’s structure. This is a sound and workable doubt early simple attempts did not take adequate account of the nature of the perturbation. The Mk 6 device in particular relied on the variation of the horizontal component of the magnetic field as the torpedo approached the target. This field variation induced a voltage in a sensing coil. The voltage triggered a thyratron which discharged a capacitor through a solenoid. The solenoid, in tum, operated a lever that displaced the inertia ring thus triggering the mechanical explore. This complex arrangement was presumably designed so that an explore, Mk 5, withouth the magnetic influence portion, but otherwise identical to the Mk 6 explore could be produced and issued to the fleet in peacetime. Security was apparently the overall motivation for this convoluted approach.
The perturbation of the earth’s field by a ship naturally depends on the inclination of the earth’s field to the horizontal. This inclination varies from 0 at the magnetic equator to 90 degrees at the magnetic poles. At NTS-Newport it is about 60 degrees. Regardless of the inclination of the earth’s field, a ship, because of the ferrous metal in its structure, causes both horizontal and vertical perturbations of the earth’s field which vary with distance and direction from the ship. The closer the earth’s field is to vertical the greater the rate of chance of the horizontal perturbation field with distance and the closer to a point directly below the keel the maximum rate of change occurs. Thus a device that senses the rate of change of the horizontal component of the perturbed field works best where the earth’s magnetic field has a large vertical component. Unfortunately, a device that works well at high magnetic latitudes may not work at all well where the earth’s field is nearly horizontal. Thus, the performance of a simple magnetic influence explore is significantly dependent on the latitude at which it is operated.
Exactly this problem affected the magnetic explorer developed by the Royal Navy, the German Navy and the U.S. Navy. The Royal Navy quickly abandoned magnetic influence devices and relied on contact explorer. The German Navy provided a sensitivity adjustment that would, in principle, compensate for changes in latitude. This was unsatisfactory and it too was abandoned fairly quickly. 12 The Buord/NTS-Newport response was first denial that there was a problem, then a complicated set of instructions for setting the explorer for different latitudes.
The magnetic influence explore was unquestionably responsible for sinking some, perhaps even a large fraction, of the 1.4 million gross registry tons of Japanese merchant ships sunk by submarines between December 1941 and August 1943. Reports from submarine commanding officers of apparent magnetic influence explore failure, mainly duds and premature, finally led to CINCPAC ordering the disabling of the magnetic influence feature on 24 June 1943. COMSUBSOWESTPAC reluctantly followed suit in December 1943. 13 CINCPAC’s order was issued 18 months after Jacobs, on SARGO’s first war patrol, ordered the deactivation of the magnetic influence portion of the Mk 6 explore in his torpedoes and incidentally got into considerable difficulty for doing so. Magnetic influence explore were not used by U.S. Navy submarines through the balance of WWII.
The Impact Exploder
Once the depth problem had been fixed and the magnetic influence feature of the Mk 6 exploder deactivated, it came the tum of the impact exploder to demonstrate its merit. Unfortunately the initial result was a plethora of duds, solid hits on targets without warhead detonations. This problem was suspected earlier, but it was not until the other two problems had been eliminated that there was unequivocal evidence of a problem with the impact exploder. This difficulty was a further frustration for the operating forces,but fortunately it was quickly diagnosed. The key to the problem was again the increased speed of Mk 14.’-‘ The impact portion of the Mk 6 exploder was exactly the same as that which had been used in the Mk 4 and Mk S exploders. The Mk 4 worked entirely satisfactorily in the 33.5 knot Mk 13 torpedo. What was overlooked was that in going from 33.S knots to 46.3 knots the inertial forces involved in striking the target at normal incidence were almost doubled. These greatly increased inertial forces were sufficient to bend the vertical pins that guided the firing pin block. The displacement was sometimes enough to cause the firing pins to miss the percussion caps, resulting in a dud. In cases of oblique hits, the forces were smaller and the impact exploder more often operated properly. Several war patrols, especially those cited above, convinced COMSUBPAC, Vice Admiral Charles Lockwood, that there was a problem and he again resorted to experiment. Firings at a cliff in Hawaii demonstrated that some torpedoes did not detonate when they hit the cliff. A rather risky disassembly of a dud revealed the distortion of the guide pins. It was a simple solution to make aluminum alloy (rather than steel) firing pin blocks and lighten them as much as possible thus reducing the inertial forces to a level that did not distort the guide pins. Another solution was to use an electrical detonator and a ball switch to fire the warhead. This too was relatively easy to implement and soon became standard.
Once these and other less significant problems were solved, the Mk 14 torpedo became a reliable and important weapon. After WWII it was modified to accommodate electrical fire control settings, gyro angle, depth and speed, and as Mk 14 Mod 5 remained in service until 1980.
How and Why
It is worth asking how these three problems might have come about and presented such a refractory situation early in WWII. It is easy to identify several contributing factors, but it is unlikely that any one of them alone was the deciding factor. One of first factors was the economy. These torpedoes were developed during the Great Depression: the total U.S. Navy budget from 1923 through 1934 averaged less than $3SOM per year and total personnel stood at about 110,000. In that environment a torpedo was valued at around $10,000 (about the same as a fighter aircraft airframe complete except for engine) and destroying one in testing was a risk that only the fearless were willing to run. The result was that testing and proofing were done in such a way as to avoid risk of damage either to expensive torpedoes or scarce targets. As is often the case, constrained testing failed to reveal certain critical problems. It is, however, difficult not to believe that deep running, in particular, should have been discovered. There were well documented reports of German and British problems during WWI. It appears also that impact exploders were not tested in high speed torpedoes or at least not tested in impacts of well simulated warheads with hard targets. Such tests were undoubtedly omitted in an effort to avoid destroying useful materiel, exploders in particular, and perhaps further justified by the fact that the exploder performed satisfactorily in lower speed tests and by its primary role as a back up to the magnetic influence exploder. Thus we conclude that with respect to these two problems, depth control and the impact exploder, the poor state of Navy finances and the concomitant lack of realistic testing probably played a significant role.
Another aspect of the situation was the almost total isolation of NTS-Newport from the larger U.S. technical and engineering community especially after 1923 when the station secured a monopoly on torpedo development and production. Political and labor interests in keeping jobs in New England probably encouraged the isolation. The net result seems to have been a lack of expansion of the scientific basis for torpedo technology at Newport at a time when dramatic changes in engineering were taking place elsewhere. No one was thinking about torpedoes from different perspectives and asking hard questions about design details. The isolation was exacerbated, especially in the case of the Mk 6 exploder, by draconian security, which in some cases even excluded the operating forces from full knowledge of the weapons they were expected to us. In this isolated environment, NTSNewport developed an arrogant we are the to do experts attitude and when problems began to arise, the response was denial-there ls nothing wrong with tM torpedoes-with the result that problems were identified and fixed slowly.
Perhaps not surprisingly a very strong polarization developed between the operating forces and the torpedo shore establishment. The operating forces resented their exclusion from the torpedo development cycle and flaunted their successes in proving that there were problems with the Mk 14 torpedo. These strongly expressed opinions of the men of the operating forces did not tend to improve relations with NTS-Newport. The operating forces also tended to exaggerate their contributions to the solution of the problems and deprecate those of NTS-Newport. A distinguished and truly great submariner recently wrote: .. So by the beginning of September 1943, the operating submariners bad detected and solved three serious defects in the Mark XIV torpedo: its faulty depth setting, skittish magnetic exploder and sluggish firing pin. All three problems bad been solved by the operating forces in their tenders and bases, without help from Newport or Washington.”This is certainly an overstatement, but what is most significant is that though written over 50 years after the events, it still reflects the intense polarization that existed between the operating forces and the torpedo shore establishment.
This spectrum of problems was not unique to the U.S. torpedo establishment. Almost the same set, defective depth control, unsatisfactory and untested magnetic exploder and a contact exploder that did not work at certain striking angles, occurred in the German Navy and many of the responses of the shore establishment to the problems were also the same. The situation is discussed in considerable detail by Doenitz in his memoirs. 17 The German Navy’s problems were closed out. however, with four senior officers being tried by court martial, on the order of Grand Admiral Eric Raeder, found guilty and punished.
Lest there be any implication that the entire U.S. Navy or even all of Buord was functioning in isolation, we note that at about the same time early experiments with what became radar were being conducted at the Naval Research Laboratory (only about 350 miles southwest of Newport). In 1937 complete disclosure of the state of radar development was made to the Army Signal Corps and Bell Telephone Laboratories. Radio Corporation of America was brought into the fold in 1938.11 The contrast of this approach to the Newport approach is nothing if not striking. Buord itself in the development of range keepers for surface fire control, in a comparably secret endeavor roughly contemporaneous with the Mk 14 development, co-opted Ford Instrument, ARMA and Sperry to assist with the development. A later dramatically contrasting development program was the development of the Mk 24 Mine (Torpedo) between December 1941 and May 1943, which is discussed in a subsequent part of this series.
This takes the story of U.S. Navy torpedoes through the beginning of WWII. As the United States became involved in the war, it became apparent that new kinds of torpedoes would be useful and a multitude of programs to develop improved weapons for submarines, surface vessels and aircraft were initiated. The idea that torpedoes could be significant ASW weapons also evolved and was elaborated with considerable success. The wartime developments and the post war development of U.S. Navy torpedoes are discussed in the third part of this series.