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During the period 1971-1972, while I was serving as Commander Submarine Division 41, I became very interested in a number. It dealt with Mk 37 torpedo effectiveness. At the time, the Mk 37 was the submarine ASW torpedo, the Mk 48 still being only in its operational test and evaluation phase. NOL White Oak published a quarterly document that laid out the probability of kill (Pk) for the Mk 37. Interestingly enough it was 0.37, and consequently easy to remember. What it conveyed was that, all other things being equal, the average submarine would need to fire three Mk 37s to be reasonably sure of a kill against an enemy submarine during an engagement. Presumably the P1c number was also used to help generate the total number of torpedoes that would have been needed in wartime in an all-out conflict with the USSR. The Mk 37 P1c number thus had two levels of significance for ASW operations, the first at the tactical level, and the second at the strategic (logistic) level.

A thorough reading of the NOL publication indicated that all Mk 37 submarine torpedo firings were used in arriving at the P1c number. Every torpedo firing that produced a torpedo firing report was an input into the NOL number. That seemed reason-able at first glance. However, on reflection I began to have second thoughts. Were all submarine torpedo firings equally valid in arriving at a P1c that would be a guide for wartime operations? The answer, of course, is a resounding “No”. When an SS or SSN completed overhaul and commenced refresher training, it turned to torpedo firing as soon as crew proficiency permitted, since that was the primary reason for its existence. However, early torpedo firing exercises, like all other exercises and drills, were rarely conducted at an advanced level. Submarine crews coming out of overhaul (or commissioning), like surface ship and aircraft crews, have to learn to walk before they can run. I dare say that most early torpedo firing exercises started with simple problems, with the target movement constrained, and the firing submarine having a fairly good idea of opening range, target speed, and direction of approach. Hits in these early exercises were gratifying to the fire control party and the torpedomen, but have little to do with the accurate estimate of a wartime P1c. As time progressed, exercises increased in complexity and uncertainty, until toward the end of the firing submarine would have very little information about possible targets.

I am not suggesting that submarine commanding officers tried to load the dice to make their division and squadron commanders think they were tactical bot shots. On the contrary, tactical training in something as complicated as a bearings only sonar approach is a gradual progression and a building up of many skills. At some point, of course, initial refresher training is over and the individual submarine reaches a state of reasonable proficiency in torpedo firing. Logically, wartime P1c determination for any weapon system should start to be measured at the end of refresher training, rather than from the beginning of refresher training.

What then was the real P1c for the submarine-fired Mk 37 torpedo? It certainly wasn’t 0.37, since some of the firings that contributed to that number were more nearly tests of torpedo tube operation and guidance wire payout performance than of sensor operation and fire control party ability to solve for target motion. Was it 0.25, or perhaps even as low as 0.20? If the latter, then it would have taken five Mk 37s per enemy submarine engagement rather than the three allocated earlier. That would be a 66 percent increase in total weapons required, a not insignificant difference. The correct answer is that nobody knew, because some of the data input into the NOL calculations was irrelevant.

The point of the discussion is that operational submariners need to look very carefully at numbers, in particular at the derivation of submarine weapon systems P1c, to ensure that they reflect the level of performance that can be expected from trained crews operating under conditions of uncertainty. We of course must provide the trained crews. Wartime and our enemies will provide the uncertainty, whether we like it or not. We should not fool ourselves by accepting calculated weapon systems P1c numbers blindly. We need to examine carefully what goes into P1c numbers calculations, and to insure that we are not getting garbage out. What is in a number is significant, both at the tactical and strategic levels.

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