In 1943 the war against U-boats in the Atlantic was beginning to be brought under control by the Allies. The
signals the Germans used to communicate with the U-boats were being read by Ultra, after the capture of the Enigma machine and the code breakers at Bletchley Park and other locations were better able to direct Allied ships and aircraft to the locations of the German submarines. The tactics the Allies used to hunt U-boats and to protect convoys were also much better than in years before, the lessons of 1942 were hard ones to learn but learn the Allies did and used every lesson to better find and kill the enemy.
In 1942 German subs sank or damaged over 1,300 ships but by Sept. 1, 1943 the count had been reduced to a little less than 500, by the end of 1943 the total for the year was less than 600, less than half from the previous year. Never again would the U-boats rampage across the sea, nevertheless they remained a constant threat to merchant ships and warships alike.
While the Allies were getting better at hunting the submarines the Germans were working on new weapons
and tactics to tip the scale in their favor. The latest weapon in the German arsenal was the T5 Zaunkönig 1 torpedo known by the Allies as the German Navy Acoustic Torpedo or GNAT for short. This torpedo was
specially designed to sink convoy escort vessels. It was tuned to 24.5 kHz which was the frequency a propeller makes on a ship traveling at about 10 to 18 knots. It traveled at about 24 knots and had a 440 lb. Hexanite warhead, it was deployed in Sept. of 1943.
Just before 5 a.m. on Sept. 20, 1943 the U-270 became the first U-boat to fire a GNAT taking aim at the
HMS Lagan K-259. The Lagan then became the first victim of the new weapon when it hit her stern. The
explosion killed twenty-eight of her crew, Lagan however did not sink but when she reached port under tow
she was declared a total loss and was later sold for scrap.
The U-270 was depth charged on Sept. 22 by one
of the escorts, the damage was so bad she had to return to base for repairs.
Lagan was one of the twenty-nine escorts for the forty ship Liverpool to New York convoy ON-202, and the
first casualty but not the last. At 09:30 two Liberty ships were attacked by U-238. The Frederick Douglass and
the Theodore Dwight Weld were both hit with conventional torpedoes, Weld sank while Douglass was
was abandoned and sunk later that night by U-645. The rescue ship Rathlin picked up all sixty-nine men and
one female stowaway from the Douglass. However she only found thirty-eight of Weld's seventy man crew,
one of them, seriously wounded, died onboard. U-270, U-238 and U-645 were part of a wolfpack consisting of seventeen boats, and this was only the beginning.
Just before 22:00 the new weapon would damage another ship, the HMCS St. Croix I-81, another of the
escorts. The U-305 fired the torpedo which, following the sound of the propeller, hit her in the stern. St. Croix
was dead in the water but failed to sink, an hour later a conventional T-3 torpedo completed the job sending
her to the bottom. One hundred and forty-eight of her crew died with her, the eighty-one survivors were picked
up by HMS Itchen K-227 the next morning. Unknown to the crew of the Itchen they had also been fired on by
the U-305 just after the St. Croix had sunk but this torpedo, another GNAT, failed to hit the target.
The new torpedo had hit two ships but failed to sink either one of them by itself, that was about to change. At
00:22 hours on Sept. 21, 1943 the HMS Polyanthus K-47, while looking for survivors from the St. Croix, was
hit by a GNAT fired by U-952, this time the torpedo destroyed the ship. Polyanthus exploded
immediately leaving only one survivor, Lt. John G. Aitken RNR, from her eighty-five man crew, he was picked
up by HMS Itchen. HMS Polyanthus became the first ship sunk outright by a GNAT. About four hours later
Itchen was again fired on this time by U-270 and again the GNAT failed to hit the target.
A few minuets before midnight on Sept. 22 another GNAT was fired, this time from U-952, the target is thought to have been Itchen although it is possible it was meant for another ship. The result, another miss. However her luck ran out less than two hours later on Sept. 23, 1943 when a GNAT fired from the U-666 finally hit the Itchen. Itchen exploded and sank, the explosion was so violent that parts of the ship landed on the U-666.
Those who were lucky enough to have survived the sinkings of St. Croix and Polyanthus did not fare so well on
the Itchen. Only three men were picked up, two from the Itchen and one from St. Croix, Lt. Aitken, the only
survivor from the Polyanthus was lost with eighty men from St. Croix and one hundred and forty-six from
Two hours after this attack the U-238 sank three of the merchant ships in the convoy in a single attack. She fired five torpedoes which sank the Fort Jemseg, Oregon Express and the Skjelbred, of the one hundred and forty-one men on the three ships only nine were killed. The final attack against the convoy occurred about 08:30 when U-952 fired on the Liberty ship James Gordon Bennett and the Steel Voyager. The torpedo that hit the Bennett malfunctioned but the Steel Voyager was sunk, her sixty-six man crew were all rescued.
Every U-boat involved in these attacks was lost during the war, the first being U-645. Still under the command
of the same man, she
was sunk on Dec. 24, 1943 by the USS Schenck DD-159 near the Azores, only three of
the fifty-five men onboard were rescued. After sinking the derelict Frederick Douglass in ON-202 the only other ship ever sunk by U-645 was the American cargo ship Yorkmar on Oct. 9, 1943.
The next day, Dec. 25, 1943 the U-666 departed Lorient, France for her fourth war patrol, under a new
commander she was never heard from again. HMS Itchen was the only ship sunk by U-666.
The next boat lost was the U-305, she sailed from Brest, France on Dec. 8, 1943 and has been missing since
It is thought she was sunk on or about Jan. 16, 1944 with all hands, including
Kapitänleutnant Rudolf Bahr, the man who sank the HMCS St. Croix. Ironically it is thought she was sunk by a GNAT that she fired, a fate shared by several U-boats until the procedure for firing them was changed.
Less than a month later on Feb. 9, 1944 the U-238 met her end southwest of Ireland when three Black Swan
class sloops, HMS Kite U-70, HMS Magpie U-82 and HMS Starling U-66 depth charged her, all fifty of the crew
were killed. The only ships ever sunk by the U-238 and
Kapitänleutnant Horst Hepp were those in ON-202.
On Aug. 6, 1944 the U-952 was sunk at Toulon, France by USAAF B-17's and B-24's during an air raid. Only
one other ship was sunk by the U-952 since the attack on ON-202, the Liberty ship William B. Woods on
Mar. 10, 1944.
The last boat lost was the U-270, the first boat to ever fire a GNAT in combat. She was bombed in the Bay of
Biscay by a RAAF Sunderland aircraft. The GNAT that she fired at Lagan was the only damage to shipping this boat ever caused however, she did shoot down two RAF B-17's in 1944.
The new weapon, the GNAT, although a breakthrough in technology, turned out to be less than successful in
combat. From deployment in Sept. 1943 until the end of the war less than fifty ships were sunk by the GNAT.