Authors: Michael Gannon
Essentially, a U-boat’s pressure hull existed as a weapons platform, that is, as a means for delivering to the enemy, sometimes overtly, sometimes in stealth, a considerable destructive threat. Although a IXC like U—515 carried two deck guns on its upper casing, a 10.5 cm forward and a 3.7 cm aft, as well as one or two 20mm anti-aircraft guns on a platform aft of the conning tower, and although some boats (notably the IXB U
-123)
had sunk shipping with gunfire alone, the World War II U-boat’s main armament was always the torpedo.
9
A IXC could carry as many as twenty-two torpedoes. Normal stowage on a
Feindfahrt
(operational patrol) was fifteen to seventeen. These cigar-shaped weapons would be stored as action-ready in the launch tubes, of which the IXC had six, four bow and two stern, and as reserves under and
over floor plates or in chains or cradles that temporarily displaced sleeping bunks in the fore and aft torpedo rooms.
Additional stowage was provided by six containers under wood slats between the pressure hull and the upper deck casing, but by 1943 U-boats rarely used them because of the length of time it required the crew to winch a torpedo down the open forward hatch, a period during which the boat was critically vulnerable. Concern was spreading by April 1943 that the Allies possessed new, more powerful depth charges, as evidenced by increased cases of damage to the upper deck containers. Should those containers fracture and fill with water, and should weight thereby suddenly increase to offset the trim, a submerged U-boat could fall fatally out of control. For this reason, as well as for the fact that the now constant danger of air attack had deterred boats from reloading at sea, BdU ordered all boats of whatever type preparing to sortie from base to leave their containers behind.
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Technically speaking, the action-ready torpedo in a tube was not “fired” during combat, for no explosive powder was ignited to serve as a propellant. Rather, the tube was flooded and the torpedo was “launched,” or “released,” by a blast of compressed air at about twenty-four atmospheres of pressure. The usual command was
Los!
(“Release!”) (It should be noted, however, that the word
shot
[Schuß] was frequently used in U-boat KTBs to indicate a torpedo launch, and the report of a launch filled out by Watch Officers was called a “Shooting Report”
[.Schussmeldung
].) Once released, the torpedo became an independent, self-propelled submarine of its own, with guidance system, engine or motor, propellers, rudders, and hydroplanes, which steered its high explosive warhead to immolation against or under the hull of an enemy ship. Its destiny was to tear a hole in that hull, causing the ship to sink. U-boat men called their torpedo an
Aal
(eel). Henke’s U-515 carried two types of eels:
T-I, G7a, “Ato”:
This torpedo, standard armament throughout the war and valued for its dependability, was driven by a gassy steam generated by a combustion of alcohol and compressed air. Power was passed through a turbine to a single six-bladed propeller. Speed settings
permitted runs of 30, 40, or 44 knots for ranges, respectively, of 12.5 kilometers, 7.5 km, and 6 km at depths below the surface prescribed by the launch officer. In daylight, the G7a left a visible surface wake of exhaust gases (bubbles). The warhead, filled with 280 kilograms of high explosive, was detonated by a Pi 3 pistol that was activated either by impact on a ship’s hull or by magnetic influence of a ship’s keel. The Pi 3-equipped
G7a.
had a tendency to explode at the end of a miss run. The “G” stood for type number; the “7” for length, 7.16 m (7.8 yards); the “a” for air-steam propulsion. Diameter of the G7a was 53.46 cm (21 inches), the same as for the British Whitehead torpedo.
T-III, G7e, “Eto”:
This type was propelled by a 100 horsepower electric motor powered by lead-acid wet cell batteries that drove a pair of two-bladed counter-rotating propellers. An improved model of an earlier electric eel (T-II), the T-III, or G7e, was the more common weapon on board U-boats in spring 1943. It had all the same dimensions as the G7a and the same warhead weight. A Pi 2 pistol allowed for both contact and magnetic detonation. The latter was the preferred setting, since, instead of releasing most of its energy upward alongside the hull in a detonation plume, it directed its major force directly upward against the keel, theoretically sinking the target with a single explosion; but see U-515’s two coups de grace with
California Star.
The T-III’s principal advantage was that it left no bubble wake to give away the U-boat’s position. Its main disadvantages were: (1) it was slow (30 knots only) with a short range (5 km), and that only if the batteries were pre-heated to 30°C before launch; and (2) the G7e—the “e” standing for electric—had to be serviced every three to five days in order to maintain its complex innards, particularly the power system.
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The U-515 was not yet equipped with the newest operational torpedo type, FAT, for
Federapparattorpedo
(spring-operated torpedo). This weapon, also called the
Geleitzugtorpedo
(convoy torpedo) was a G7a (“Atofat”) or G7e (“Etofat”) fitted with a guidance system that caused it to take a direct course for a given range toward a convoy’s ship columns, then to turn right or left and describe a succession of long or
short legs, or loops, the expectation being that a snaking, to-and-fro course through the columns would result in a random
Treffer
, or hit. FATs, which the British called “Curlies,” were still not common equipment in spring 1943. The U-515 would not receive FATs until her fourth cruise, beginning 29 August, when she would also carry another new torpedo type, introduced the previous February and March, the acoustic anti-escort T-V, G7es, called
Zaunkönig
(wren), which was designed to home in on the cavitation noise (24.5 kHz) of an escort vessel’s propellers running at 10 to 18 knots. This type, which was even rarer than the FAT on U-boats at sea in spring 1943, would have its first success in combat in September.
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Most of the officers and crew who launched U-515’s eels had served together since the boat was commissioned. In that respect they were unlike the typical crew, some of whose enlisted members normally transferred out of a boat following two patrols in order to take the classwork and training required to qualify them for a new specialty, higher grade, or both, after which they would be assigned to different boats. Somehow, Kptlt. Henke had avoided that rotation, with the result that he commanded an unusually high number of experienced twenty-two-year-olds at a time when the average age of non-petty officer crewmen was a year or two younger.
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Furthermore, at the date of commissioning, Henke had inherited a cadre of petty officers (23 years old and older) who had had prior experience on Type IX boats.
This veteran crew, most of them U-boat volunteers, was motivated, we may believe, not only by the usual inducements of proud service in an elite arm; education in the latest technology, specially high pay rates, including combat patrol bonuses; the best rations to be found in any of the German services; generous leaves; and the near-certainty of medals, including Iron Crosses first and second class; they were also motivated by the success of their Commander in sinking ships, for
that
was the particularly energizing tonic on a U-boat. Many negative distractions could be set aside, for example, lack of promotion opportunities because of the crew’s continuity of service on this particular boat, Henke’s sometimes severe disciplinary responses to minor crew infractions,
or the festering personality conflict between the Chief Engineer and his senior engine room machinist—all of that mattered little if the boat was going from success to success with her torpedoes. When, at last, U-515 succumbed to U.S. Navy destroyers on 9 April 1944, American interrogations of her survivors disclosed that even at that date, when the Atlantic war was long before lost, morale aboard U-515 remained high.
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The thirty-three-year-old man who commanded
Fünffünfzehn
(515) was one of the most enigmatic and troubled Commanders in the U-Bootwaffe. Hardly the one-dimensional German type, he was an amalgam of conflicting traits. On the one hand impetuous, even hotheaded, in his performance of duty he was the model of professional cool. Uncomfortable under naval discipline himself, he was quick and rigorous in imposing it on others. Outgoing and gregarious by nature, he was viewed by his fellow officers as a vainglorious loner. Respectful of the Nazi state, which, among other things, punished Germans who listened to American popular music, he loved jazz and kept an impressive collection of Cole Porter songs on phonograph records. In stature he was five feet nine inches in height, 175 pounds. Good-looking, blueeyed, he was always the impeccably attired
schöner Henke
—“Handsome Henke.”
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Disciplinary problems dogged the young officer during a career which, from his entrance into the Navy as an officer cadet in 1934 up to the outbreak of war, was spent mainly on shore assignments, except for two tours amounting to fourteen months on the pocket battleship
Admiral Scheer.
In March 1940, he was ordered to the U-Boat School
(U-Schule
) at Pillau, East Prussia (now Baltiysk, Russia). Pausing in transit at Berlin to visit a girlfriend, Henke ended up late on arrival— Absent Without Leave—by two days. Though the AWOL charge resulted from a misunderstanding of his due date, he was court-martialed and sent to duty with a punishment company. Finally allowed to complete his studies, he was assigned in November 1940 as a Second Watch Officer
(Zweiter Wachoffizier
, or II.W.O.) to the Type IXB U
-124,
based at the newly occupied port of Lorient on the Brittany coast of France. It was there that he learned that because of his spotty
disciplinary record, he had lost all seniority and would have to rebuild his career from the bottom.
In four patrols on U
-124,
during which he advanced to First Watch Officer (I.W.O.), Henke not only redeemed his reputation but proved himself an excellent candidate for Commander’s School at Danzig (now Gdansk, Poland), to which he was assigned in November 1941. Following two months of intensive instruction in command responsibilities, simulated attack procedures, and the newest torpedo technology, Henke reported to the Deutsche Werft yards in Hamburg-Finkenwerder to assemble his crew and take command of U—575. The successes achieved during his first two command patrols with the new IXC earned him restoration of his seniority on the career list, promotion to
Kapitänleutnant
(Lieutenant), and the award of Germany’s highest decoration, Knight’s Cross of the Iron Cross.
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He was the seventieth U-boat officer to win the coveted
Ritterkreuz.
Henke, his crew, his boat, and his torpedoes were fully primed for the steamy equatorial night of 30 April/1 May off West Africa.
On 13 April, after finding little else off Dakar besides
Bamako
, which he sank on the 9th, Henke steamed southeast past Portuguese Guinea (now Guinea Bissau) to take up a new position southwest of the busy port of Freetown, in Sierra Leone, which he reached on the 16th. But for nine days after that date, no ship traffic appeared either shoreward or seaward—a “sour-pickle time.” Nor did the conning tower bridge lookouts sight so much as an aircraft during that same period. Then, on the 25th, two British Royal Air Force (RAF) Short Sunderland flying boats came into view. Two days later, lookouts sighted a merchant vessel’s smoke, but another flying boat, this time a RAF PBY-5 Catalina flying boat, of American design and manufacture, forced the boat to dive and fall behind the contact. Better luck, it seemed, came in the late morning of the 28th, while U-515 was submerged to avoid possible morning air reconnaissance. The hydrophone (
Gruppenhorchgerät,
or GHG), which was an underwater passive sound detection device, picked up the sound of explosions from two series of depth charges, as well as the
swish-swish-swish
of warship propellers. Henke came to
periscope depth and made an observation of one “London” type cruiser, four destroyers, and two passenger ships, which he assumed were filled with troops, steaming on a course of 340° (toward the northwest) at 12 knots.
Since it was daylight, he decided to make a submerged attack. The range was 5,000 meters. That would be a stretch for his Eto wakeless eels, but Henke ordered a double fan-launch
(2er Fächer)
from forward Tubes I and IV, with depths set to 3 and 5 meters. Both eels missed and, after eight minutes, detonated at the ends of their runs. The sourpickle time continued. And, on the 29th, U-515 had the unpleasant experience of being surprised by an RAF Catalina that dived on the boat out of dark cloud cover. The 20mm anti-aircraft gun abaft U-515’s tower gave a good account of itself with about ten hits on the Catalina, which, thrown off its stride, dropped five depth bombs harmlessly astern. After which—
ALAARMM!
—the boat dived, as it would have to do twice more that evening when probing Catalinas came again.
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Daytime on the 30th passed uneventfully. The morning was spent submerged. Crew members who were not asleep went about their usual duties, tending to the Eto mechanisms, checking the battery arrays for chlorine gas buildup, monitoring the wireless telegraph (W/T) receivers and hydrophone, oiling the rocker-arm hinges on the nine cylinder MAN diesels, filling out report forms, studying for qualifying exams, cooking the midday meal, or shaving—Henke was one of the few commanders who forbade beards. No man wore more than shorts because the tropical temperature inside the boat exceeded 100 degrees Fahrenheit.
At 1345 German Summer Time (GST), which all boats observed no matter what their position at sea, and which was two hours ahead of Greenwich Mean Time (GMT), U—515 blew tanks and surfaced to air out the noxious and foul-smelling interior. The lookouts searched the ocean’s edge for smoke plumes, but there were none. After fifteen minutes, the boat resumed an underwater listening station, until 2041, when Henke ordered the boat surfaced again so that he and the bridge watch could survey the horizon in the day’s last light. Twenty-one minutes later, a lookout seized like a bird dog and exclaimed,
“Herr Kaleu!”
the diminutive of Henke’s rank. Following the lookout’s point, Henke drew into the lenses of his Carl Zeiss 7 x 50 binoculars the murky images of smoke clouds where the ocean met the sky shoreward to the southeast. He estimated the smoke at range 15 nautical miles, bearing 145°. Gradually, the images sharpened and mast tops became visible, then funnels and bridge screens. Henke counted fourteen large, fully laden merchant ships in convoy, average tonnage 6,000–7,000 GRT, proceeding northwest, guarded by what appeared to be three destroyers and five other escort vessels.
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Actually, the convoy, designated TS.37, was composed of eighteen merchant vessels protected by only three escorts, the smallest in the Royal Navy’s inventory: the corvette H.M.S.
Bellwort
and two trawlers. The convoy’s five columns had originally included a nineteenth merchant ship, but two days before she had left the formation to proceed independently, accompanied by a third trawler.