like the airplane, a tool for whittling down the enemy battleline before it could confront the American heavy ships. American submarine tactics developed for attacking fast and well-defended warships were too cautious, relying on submerged and even futile, “blind” sonar attacks. Escort tactics suffered, too; shepherding destroyers, trained to defend fast warships, whose high speeds were nearly proof against successful attack under normal conditions and whose turbulent wakes fouled sonar equipment, became complacent and inefficient in escort technique. Without slow, unruly merchant convoys to escort in peacetime, there could be little useful antisubmarine warfare and escort doctrine, for doctrine must be built on experience. Hence, there was no agreement on such basic matters as the most effective escort formation, the optimum distance between the screening ships and the convoy, whether the escorts should patrol station, when to leave the convoy unprotected in order to dog a contact, the efficacy of illumination, precise search and attack procedures, and many other significant points of escort technique.23
Small escorts such as subchasers had been improvised during World War I, and many, including President Roosevelt, felt that the experience could be easily repeated, if necessary. Once Admiral King warned the President,” Nothing remains static in war or in military weapons, and it is consequently often dangerous to rely on courses suggested by apparent similarities in the past.” Admiral King was right. The World War I U-boat had been forced by its limitations to operate in the immediate approaches to the United Kingdom, where interception was easiest. Hence, escorts operated out of Queenstown on relatively short trips, not having to cross the ocean, and the strain on men and ships was small. In World War II, however, escorts had to have the size and endurance to fight in mid-ocean.
The General Board of the Navy rejected various escort prototypes in the prewar years because they were almost as expensive to build as destroyers, yet nowhere as efficient or versatile. Corvettes were too slow; “Treasury”-class cutters and destroyer-escort types lacked the speed, ruggedness, versatility, and firepower of modern destroyers, and specialized escorts were not always economical—one modern destroyer could be built for less money, for example, than two proposed 875-ton antisubmarine warfare vessels. Hence, the Navy preferred to invest in the better ship, but lacked a cheap, easily produced, specialized antisubmarine type at the outbreak of war.24
Also, antisubmarine warfare was dependent upon World War I weapons. Depth charges had rarely been lethal in individual patterns, most submarines having been sunk by accumulated damage over long periods of attack; evidence of World War I showed that 1,000 depth charges had been expended for each U-boat sunk. Experience indicated that about 2½ hours of persistent attack were required to kill a submarine, and that it would require a pattern of forty depth charges to ensure the destruction of a located submarine. But of course, lack of means to drop depth charges as fast as that or to carry a sufficient number on ships made such huge patterns impossible.
Not only was sonar gear affected by the salinity and temperature of the water, ships’ wakes, currents, fish, and debris, but the beam broke contact in the crucial attack run because the angle of the sound cone passed above the target as it was neared. Furthermore, the echo increased as the target was closed, causing the operator to believe he was on target when actually the submarine might be edging to the outer limits of the sonar beam.25 But, as one officer noted:
Given a true contact and a skilled sound operator the problem is still only half solved. The conning officer of the destroyer must make an accurate “landing” on an object which he cannot see and which is attempting to evade him. He must “lead” the submarine about 15 degrees as he closes to 500 yards, then order flank speed, and decrease the lead as his speed increases. Conning and timing an accurate attack requires excellent teamwork between sound operator and conning officer, which can only be developed by practice against a submarine.26
But destroyer practices with “live” submarines were rare; and the Key West Sound School could not adequately prepare men for the dismal water and weather conditions of the North Atlantic. As late as 1938, some destroyers had not been fitted with depth-charge racks, indicating the casual, complacent approach to antisubmarine warfare.27 The CO of one destroyer division, noting that only two of his ships had depth charges and racks, observed, “The use of depth charges in time of war may assume great importance. . . . The theory of making depth charge attacks is well known . . . but until the practice is actually carried out, the details are usually not known and study of the problem is usually not attempted due to other more pressing work.”28
Depth-charge battle practices usually ended with the destruction of the submarine, but these successes were artificial. They were based on certain “knowledge that a submarine was actually present in the near vicinity,” and often pitted a team of five destroyers, unhampered by an array of slow, vulnerable merchant vessels, against a single submarine. It was noted that in problems where surprise was possible, the destroyers “have not shown corresponding proficiency.”29 In one practice, an attacking destroyer failed to measure the changing relative speed and bearing of the target and dropped depth charges well away from the submarine. Her companion destroyers dropped depth charges “apparently at random,” with one charge, the official report caustically noted, “accidentally dropped . . . on the submarine.”30
One prewar tactical exercise will illustrate the problems of antisubmarine warfare. In the spring of 1939, seven destroyer divisions exercised off Guantanamo Bay with “live” submarines.
The ships of Destroyer Division 2 failed to locate the S-42. They searched at too high speeds and thus did not hear the submarine. After slowing down, the Dale passed only 900 yards to port of the submarine, but was echo-ranging in the opposite direction at the time and did not detect her quarry.
DesDiv 3 located the Perch, but the submarine increased speed after the sonar gear lost contact, and the destroyers made their attacks too far astern; one destroyer attacked too soon and steamed into a predecessor’s dummy barrage. Then the submarine turned away to starboard, creating wake-turbulence under water; the destroyermen echo-ranged on the wake, the Perch soon passed beyond the sound beam, and the destroyers lost contact.
DesDiv 4 picked up the Seal quickly and pressed home successful attacks. This was an excellent division, consistently scoring well in gunnery, too; the good ships were the Smith, Cushing, Perkins, and Preston.
DesDiv 7 found Skipjack quickly, but the submarine reduced speed, and Blue passed ahead of her; the next destroyer attacked Blue’s wake. The Fanning’s pattern was closer, and the Blue then attacked on target; the Mugford’s pattern missed astern, and Patterson could not get an attack off in time.
DesDiv 8 turned in an average performance. The Cummings found S-43, and the Dunlap and Gridley made competent attacks, but the Bagley depth-charged Gridley’s wake.
DesDiv 11 found the Stingray, but the submarine increased speed, sending out “knuckles” of water turbulence, which two of the destroyers attacked. The Henley underestimated the target’s speed, and attacked astern; McCall failed to “lead” the target sufficiently, neglecting to allow for the time it took the depth charges to sink.
DesDiv 17 did not locate S-43 at all, because of excessive speed, sporadic echo-ranging, and deteriorating water conditions.31
But such valuable practices were too rare, and fear of accident and personnel losses precluded realistic night destroyer-submarine training. When in January 1941 five old, slow, and cranky “S” boats “sank” three destroyers in an exercise off Panama, it was partly because none of the destroyers had ever worked with submarines before.32 After another practice, the CO of a destroyer squadron reported that because of lack of training with “live” submarines and the newness of his skippers to their ships, his destroyers
had
