Blackett's War by Stephen Budiansky

Author:Stephen Budiansky [Budiansky, Stephen]
Language: eng
Format: epub, mobi
ISBN: 9780307962638
Publisher: Knopf Doubleday Publishing Group
Published: 2013-02-19T05:00:00+00:00

Blackett emphasized the need for scientists in this role to steer clear of “technical midwifery” so they could focus on current operational questions.

Williams jumped right into the most basic such question of all: why were the aircraft of Coastal Command sinking so few submarines? Even with the change from the 100-pound antisubmarine bomb to the 450-pound depth charge, results had scarcely improved. As of May 1941, Williams found, aircraft had sighted U-boats 200 times, carried out attacks in 130 of those cases, and definitely sunk a total of 2 U-boats—a 1 percent success rate. In most of the attacks, the U-boat had spotted the aircraft first and had time to dive by the time the aircraft arrived in position to drop its depth charges. Coastal Command’s Tactical Instruction No. 12, issued January 27, 1941, was based on a straightforward calculation: it took the average time a U-boat had been out of sight at the instant of attack—about 50 seconds—multiplied that by the U-boat’s dive rate of 2 feet per second, and concluded that dropping a series of depth charges set to explode at a depth of 100 to 150 feet would be most likely to catch the submerged boat. Because the U-boat could also have traveled as much as 1,000 feet forward during the same time, the orders also advised dropping a “stick” of four charges spaced horizontally at about 250-foot intervals, to try to blanket as much of the possible target area as possible.9

Williams had little difficulty putting his finger on the trouble once he started sifting through the data. Shooting for an average guaranteed the worst of both possible worlds. In cases where the target was at the same depth as the depth charge setting, its odds of still being on the same straight-line course last seen on the surface were almost nil: the boat would have had time to veer to the left or right, and the possible area in which it might be lurking was so vast as to be impossible to saturate with charges. Williams calculated that the average error in aim point was at least 300 feet, well beyond the 25-foot lethal radius of a 450-pound depth charge. On the other hand, the boats that had been late to react to the aircraft’s approach, and were thus still close to the surface and not far from the position where they submerged, were being attacked in the right place but with depth charges set to go off far too deep to do any damage. The 250-foot stick spacing was likewise thrown away on U-boats which had been out of sight for a quarter of a minute or less, which were sure to be within a radius of 150 feet of their last observed position. In other words, targets that were at the right depth were almost certainly in the wrong place; targets that were in the right place were definitely at the wrong depth. Williams summarized this conclusion at the very top of the first

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