Black May

by Michael Gannon

  At 1300 on the 9th, thanks to BdU’s new dispositions, U-359 (Oblt.z.S. Heinz Förster) of the Rhein group sighted the main body in 41°09'N, 26°54'W and, on BdU’s order, became its shadower. The U-boat’s transmissions were DFed by Broadway, who sent the corvette Primrose down the bearing, where she got a sighting and, after the boat dived, dropped a ten-pattern, with no evidence sequent. Meanwhile, Chavasse ordered the convoy to alter course 40° to starboard. More HF/DF bearings were acquired later in the day, suggesting that at least two U-boats were in contact with the convoy, but no sightings resulted, and because of the continued milky air, the nine Swordfish and one Martlet of 811 Naval Air Squadron aboard Biter, steaming on station astern, could not assist in the hunt. (There had been three Martlets originally, but on the 7th two Martlets had failed to return from patrols, though vigorous efforts were made to home them back. Lost, they both made forced landings alongside ships, a straggler and a trawler, and their pilots were picked up. The two ships were 90 miles northeast of the convoy! Three days later, a Swordfish was lost and its crew rescued in exactly the same way.)

  The next morning, the 10th, in slightly more diaphanous air, U-403 (Kptlt. Hans Clausen), following C2's tug on the surface, sighted the convoy, and at 1647 was sighted herself to starboard by the escort screen. Two corvettes made revolutions after the intruder, and Biter was able to launch Swordfish “M,” which reached the still-surfaced boat six miles distant before the corvettes. Raked by machine-gun fire when 1,500 yards from the conning tower, the fabric-skinned biplane banked hard out of range; then, as the U-boat dived, it returned to the attack at maximum speed of 120 knots, approaching from the U-boat’s port quarter at an angle of 45° to track, and from a height of 60 feet dropped four Mark XI D/Cs set to 24 feet and spaced 60 feet apart. They missed astern. The surprised U-boat, having survived the attack, signaled BdU that she had been engaged by a wheeled aircraft. This was certainly news to BdU, which had just signaled the Rhein boats that they need not fear aircraft, since the convoy was out of the range of shore air bases, so BUT LITTLE AIR CAN JOIN THE CONVOY.9 But Biter s flight deck, built on an American merchant hull, had been able to offer the ultimate surprise, a hard-surface landing gear aircraft flying from a midocean runway.

  The escort carrier (CVE) was a warship type coincidentally first produced by both the RN and USN in June 1941. In both instances a flight deck was mounted on a merchant ship hull. The RN type, H.M.S. Audacity, embarked six Martlet fighters on the converted merchant ship Hannover captured from the Germans. Assigned to the U.K.-Gibraltar convoys, she had an outstanding six-month career, destroying five Luftwaffe aircraft, sighting nine U-boats, and on 17 December 1941 sharing in the sinking of U-131 (Korv. Kapt. Arend Baumann) with the 36th Escort Group (Cmdr. Frederic John Walker, R.N., SO), though the attacking Martlet and pilot were lost to the U-boat’s gunfire. While escorting Convoy HG.76 on the night of 21–22 December 1941, Audacity was struck by three torpedoes from U—751 (Kptlt. Gerhard Bigalk) and sunk.10

  Her American counterpart, carrier U.S.S. Long Island, capable of embarking twenty-one aircraft, would not see action in either the Atlantic or the Pacific theaters but spend her career in ferrying, training, and experimental duties. But beginning in 1942, the USN heavily committed funds to the CVE program, and American shipyards began turning out large numbers of improved carrier conversions from merchant hulls, eventually producing 128 by war’s end.11 British yards produced five. Many of the early U.S. CVEs went to the RN, which made additional modifications, mainly to the avgas fuel systems to prevent vapor explosions, and two of these, Biter and Archer, were in active service on the Atlantic convoy routes during Black May. Swordfish “L” from Biter had earlier, on 25 April, shared in the destruction of U-203 (Kptlt. Hermann Kottmann) along with the destroyer H.M.S. Pathfinder, while both ships were with EG5 supporting EG B2, the close screen of Convoy ONS.4. The aircraft’s principal contribution to the kill was two well-placed calcium sea markers, since her two D/Cs dropped 20 seconds after submergence apparently did not damage the U-boat. On 10 May, Archer, with Fourth Escort Group, was supporting EG B6 with Convoy ONS.6.

  British naval historian David Hobbs has commented on the relative merits of shore-based and naval-embarked aviation at that period. Most of the flying hours of the former, he points out, were expended in transit to and from their patrol areas rather than in patrol itself. Add to that the fact that significant numbers of shore-based bombers and crews had to be kept in constant rotation on successive legs to and from the convoy, and the economy of carrier aircraft, which were based constantly with the convoy, becomes apparent. Furthermore, Coastal Command aircraft did not always successfully rendezvous with their designated convoys; in 1942, for example, 34 percent of all Coastal sorties were Not Mets. Finally, unlike bombers from afar, the carrier aircraft lent themselves to rapid and flexible tactical use by the escort commander, the attack on U-403 being an apt example.12 The only problem at this date, apart from pilots’ tendency to get lost navigating, was the inadequacy of the Swordfish aircraft in speed and structural strength.

  Following the action against this boat, BdU decided that the main body of Rhein must be 90 miles behind the fast convoy, with little chance to catch up. Accordingly, it ordered that group, excepting U-403, to withdraw from the operation against HX.237 and to move instead against the slower SC.129, which was “considered to offer better chances of success.” The fast convoy would be left to the shadower U-403 and to the six boats of Drossel closing from the east.13 The daylight hours of 11 May were quiet, though HF/DF activity increased, and Chavasse sent two destroyers ahead to probe for threats, and two of Biter’s aircraft searched the convoy’s perimeter. Later in the day, U-436 (Kptlt. Günther Seibicke) of Group Drossel found HX.237 BD 9554 (44°15'W, 27°25'W). Another of Drossel’s boats, U-89 (Kptlt. Dietrich Lohmann), reported the presence of carrier-type aircraft circling overhead—either a confirmation or a first disclosure to BdU that the aircraft that attacked U-403 was carrier-borne.

  At 2013, another of Biters aircraft, Swordfish “L,” caught U-436 on the surface and attacked her with four D/Cs from 150 feet. During the run in, the “Stringhag,” as the frail biplane was called by pilots, took heavy anti-aircraft fire, but the pilot and gunner watched the tracers pass harmlessly between the port upper and lower wings, and the pilot returned fire with his front gun. Following the D/C drop, the pilot climbed to make a return run, but after he got the slow-gaited craft around, the U-boat had disappeared. The pilot dropped a smoke float and resumed patrolling.14 At 2100 U-89 reported the convoy on a new course, 000°, or due north.15 Contact was not resumed until daybreak on the 12th, when the surfaced Drossel boat U-230 (Kptlt. Paul Sieg-mann) sighted the ship columns in heavy swell astride BD 2826, confirming that the convoy, estimated at 9.5 knots speed, had made an evasive turn to north.16 Soon afterwards, U-230 found herself under attack by the first Swordfish to make it off Biter s bucking deck that high seas morning, which was the twenty-third birthday of U-230's First Watch Officer (I.W.O.) Herbert A. Werner, a native of the Black Forest region of southern Germany, who was commanding the bridge watch:

  “Aircraft astern!” It was too late to dive. The single-engine plane came in low in a straight line exactly over our wake. I fingered the trigger of my gun. Again the gun was jammed. I kicked its magazine, clearing the jam. Then I emptied the gun at the menace. The mate’s automatic [machine gun] bellowed. Our boat veered to starboard, spoiling the plane’s bomb run. The pilot revved up his engine, circled, then roared toward us from dead ahead. As the plane dived very low, its engine sputtered, then stopped. Wing first, the plane crashed into the surging ocean, smashing its other wing on our superstructure as we raced by. The pilot, thrown out of his cockpit, lifted his arm and waved for help, but then I saw him disintegrate in the explosion of the four bombs [D/Cs] which were meant to destroy us. Four violent shocks kicked into our starboard side astern but we left the horrible scene unharmed.17

  This loss had a sobering eff
ect on Biter, who decided that antiquated Swordfish should no longer engage in gunfire duels with U-boats, despite their crews’ keenness to do so. Henceforth, the Sword-fish were to attack only with D/Cs when the U-boat was seen to be diving or had just dived. In other cases the pilot was to keep the U-boat in observation and, if possible, call in surface ship assistance. Biter s next attack would include an excellent example of called-in assistance from Broadway and the frigate H.M.S. Lagan. At 1230, in good weather, visibility 20 miles, Swordfish “B” sighted a wake, then a U-boat distant four miles, proceeding at 12 knots on a course of 060°. At about the same time, the U-boat—it was U-89—sighted the aircraft, altered course, and dived. By the time the Swordfish got down to 50 feet and dropped four D/Cs, U-89 had been under for 30 seconds. The pilot returned to the position, saw no evidence on the surface, dropped a smoke marker, and reported the action by R/T. Broadway received the report and closed the position at 24 knots, while the Swordfish returned to Biter short of fuel.

  At 1301 Broadway reached the marker and, her asdic dome lowered, obtained a contact bearing 045°, range 1,500 yards. Chavasse decided on a Hedgehog attack, which he delivered just as U-89 accelerated across his bow. There were no explosions. Lagan, in the meantime, had arrived to assist and she now made two unsuccessful Hedgehog attacks of her own. Ten minutes later, Broadway regained strong echoes on which to fire a second 24-projectile salvo, with a deflection of 15° right. This time, at 1359, there was a single sharp explosive CRACK! that was felt throughout the ship. Twenty seconds later, a second, muffled explosion was heard, and a marker was thrown overside.

  Lagan made two Hedgehog attacks on the position without result, but forty-five minutes after Broadways hit on the U-boat’s hull, wreckage appeared on the surface. It consisted of a piece of wood with an electric light switch, two positions for plugs, and the identification “Schlüssel-M” (Enigma machine); several pieces of laminated wood varnished on one side and painted white on the other; a woolen jersey with a Nazi emblem; and various other articles of clothing that were not picked up. The single Hedgehog projectile had drilled a fair-size hole. No bodies were seen. They were all entombed below in the Type VIIC iron coffin.18 And the burying for that day was not over. Within the same hour as Broadway s puncturing hit, another Drossel boat was gored; subsequendy it would flail about wounded, call desperately for help, then die gamely from the last penetrating effects of a weapon never before used at sea. Ironically, U-89 was on her way to help that boat when death chose her first.

  On 10 December 1941, three days after the attack on Pearl Harbor, the U.S. National Defense Research Committee (NDRC), acting on a proposal made to it sometime before by the U.S. Navy, convened a Top Secret meeting of scientists and engineers at Harvard University to consider the feasibility of a low-weight airborne anti-submarine acoustic homing torpedo. The feasibility agreed upon, the participants met again two weeks later to draw up general requirements and assign responsibilities for design and testing. The requirements in sum were that such a homing torpedo should be able to detect, track, and impact a source of underwater noise, such as the twenty-four-kilocycle sound produced by cavitation—the sudden formation and “popping” of the bubbles created by a high-speed marine propeller; be of a size to fit in existing bomb bays or on a 1,000-pound bomb rack; be droppable from 200 to 300 feet from an aircraft in level flight at airspeeds between 120 and 150 knots; be propelled electrically by a lead acid storage battery at 12 knots for five to fifteen minutes; and be able to carry a 100-pound high-explosive charge.

  Bell Laboratories, a division of the Western Electric Company, and the Harvard Underwater Sound Laboratory (HUSL) agreed to pursue independent but cooperative and information-sharing development of the general design. The General Electric Company would design the propulsion and servo motors (and it may also have developed parts or all of the hydrostatic depth-control system). A lightweight 48-volt, shock-resistant, lead-acid storage battery was developed by the Electric Storage Battery Company.19 HUSL measured the “self noise” made by the torpedo’s own propeller and solved the problem of allowing for it; though this was not the problem it might have been, owing to the participation of the David Taylor Model Basin at the Washington Navy Yard. There, Dr. Karl Schoenherr, after discussing prop noise for twenty minutes with Bell Labs visitors, whipped out a large piece of paper and drew a propeller design freehand. “Here is your prop,” he said, presenting the sketch of a propeller with a 14¾-inch diameter and a 12-inch pitch. When the Bell Labs people protested that these were hardly the precision specifications they required, Schoenherr had a draftsman make a more exact, scaled, dimensional drawing and, after lunch, presented that instead. Not only did the design well serve the prototype acoustic torpedo then under construction, it was not improved upon until five years after the war was over.

  The sometimes improvisational character of the torpedo’s development was further demonstrated when, for the midsection casings of the torpedo body, Western Electric and Bell Labs engineers turned to a bathtub manufacturer “whose most precise measuring instrument appeared to be a wooden yardstick”; but the company made and shipped interchangeable sections that were remarkably free of defects.20 In the end, the only significant difference between the Bell Labs and Harvard configurations of the torpedo were the type and placement of the sound-receiving hydrophones. In the Bell Labs model, Rochelle salt crystal hydrophones were arranged symmetrically around the circumference of the torpedo midsection. In the Harvard model, magnetostriction hydrophones were mounted on the nose section. While there was no meaningful difference in the performance of the two systems, it was decided by the NDRC to go with the Bell model, since the nose section containing the 92-pound warhead of HBX—1 Torpex high explosive and Mark 142 impact fuse in the forward 14½ inches of the weapon could then be handled independently and, in operations, be attached just before the torpedo was mounted on an aircraft. The four acoustic sensors, left, right, up, and down, homed to the noisemaking target by body shadow. The hydrophone on the right side, for example, did not hear the noise to the left, or port side, which was shadowed by the torpedo’s body, hence the torpedo’s guidance system turned the torpedo to port. The up and down sensors acted in the same way along the depth axis.21

  Prototypes of the torpedo were tested by both boat launches and aircraft drops to measure and verify performance characteristics. The principal testing was done at Solomon’s Island on the deepwater Patuxent River in Maryland and at Key West, Florida. At the latter site a USN submarine with a protective cage built around its propellers served as a target for air-launched homing torpedoes loaded with plaster instead of explosive. After the first three of six torpedoes banged into the propeller cage repeatedly until they broke themselves apart, the Captain in command of the exercise called a halt to the testing, reminded everyone present of his secrecy oath, and advised USN personnel involved to stay out of submarines!22

  With testing completed, the design was frozen in October 1942, and production under sole contract was awarded to the Western Electric Company. The first production model was delivered to the USN in March 1943, a remarkable fifteen months since conception. It measured 19 inches in diameter, 84 inches in length, and weighed 683 pounds. Its maximum speed underwater was 12 knots, more than adequate to overhaul a U-boat at its best submerged speed. In fact, its operating characteristics were very close to those first proposed in December 1941. Since the midsection hydrophones had maximum sensitivity in a direction at right angles to the sound source, it was not expected that the Bell model chosen, having reached its preset depth, would head directly, nose-first, at the target, even if dropped along the submerged U-boat’s track. As a USN operations research study reported in August 1946:

  The torpedo is fitted with a wooden spoiler ring and tail stabilizer to aid its flight in air; these break off when it enters the water. After water entry the torpedo usually circles, with a turning radius of 50 to 150 feet, at a depth below 40 feet, until it comes within the sphere o
f influence of a sound source sufficiently intense to activate the controls. Thereafter the torpedo proceeds on an approximate pursuit course until it strikes the target (or loses it). At full battery capacity it will run from 12 to 15 minutes, traveling approximately 6,000 yards, after which it will sink, since it has no negative buoyancy.23

  From this description, it is little wonder that airmen nicknamed the weapon “Wandering Annie.” But its official designation, to mask the Top Secret nature and purpose of the device, was Mark XXIV Mine. (Another reason for use of the term mine, it has been suggested, was to keep the weapon out of the ponderous USN torpedo establishment with all its baggage.24) It also was called FIDO, and when that was thought too closely to suggest “sniffing,” the code name was changed to PROCTOR. From the beginning, Mark XXIV was cloaked under the strictest official secrecy, since if word of its function leaked to the Germans, all a U-boat had to do in order to avoid its fatal sting was to proceed at slow submerged speed after diving, when cavitation would fall below the sound sensors’ threshold. When a manufacturer’s lot of Mk.24S was ready for shipment from Kearny, New Jersey, it was kept hidden and loaded on military aircraft in off-ramp, secure areas. Usually a guard of one officer and five technicians accompanied the lot until it reached its destination, either USN or RN.