U-31 had been been sunk on 11 March 1940 whilst on sea trials off Germany. A Blenheim bomber had caught her on the surface and attacked her with four semi-armour piercing bombs. Two of these had hit the U-Boat, damaging the compressed air tanks. Uncontrolled compressed air flooded into the U-Boat as it crash dived and killed the entire crew, apart from two in the conning tower who were washed overboard and drowned during the attack. 58 men died in total.
U-31 was spotted on the surface at 10.15am on Saturday 2nd November by HMS Antelope, a destroyer escorting convoy OB237. Her commander Willfried Prellburg was below having breakfast. Although U-31 dived HMS Antelope put in an immediate depth charge attack which damaged her slightly. The hunt was on and HMS Antelope searched for her on Asdic and again damaged her with an attack at 1113.
British Naval Intelligence was able to piece together the following sequence of events using interviews of the survivors alongside the report from HMS Antelope.
After searching in vain for nearly an hour, the Captain of Antelope decided to close the position of the last known contact.
At 1320 contact was regained right ahead at a range of 2,500 yards. The position was closed. The U-Boat proceeding at a depth of 50 metres (164 ft.) had heard the movements of Antelope and the Germans were alarmed at the destroyer’s sudden return. A full pattern of six charges set to 250, 350 and 500 ft. was fired at 1330.
This attack caused considerable damage to U 31, who, in the opinion of her engineer officer, had gone deeper, probably to about 70 metres: she went down by the stern and “full ahead” on both motors was ordered; the crew went forward and squeezed together as much as possible, but the U-Boat remained 15° down by the stern. The depth pressure gauge was still functioning, but all other instruments were out of action.
The German Captain wanted to surface but after some argument was dissuaded by the Engineer Officer.
A large bubble of air and oil rose to the surface. Range was opened and Antelope regained contact immediatelv with no doppler but marked hydrophone effect. The target appeared to be moving slowly and bubbling noises were heard, as though tanks were being blown.
A fourth attack was carried out at 1341, but only three charges with deep settings were ready. This was again an accurate attack.
The U-Boat, becoming rapidly heavier and sinking with her stern down, was at a depth of about 95 metres (312 ft.). The after torpedo tube and the Diesel air shaft filled with water, a compressed air bottle broke and the air escaped with a bubbling noise, the valves leaked, and the Captain knew that the U-Boat was making an oil track. At 1344 large bubbles came to the surface.
At 1350 U31 surfaced right astern of Antelope. The Destroyer’s after group opened fire, until the crew were seen to be abandoning ship. The U-Boat’s motors were left running ahead with port wheel on, speed about 4 knots. Antelope’s whaler tried to board, but the U-Boat’s speed was too great, and as it was not quite certain whether all the crew had left U 31, fire was opened again at 1405. Twenty-three rounds were fired but owing to the large swell no hits were obtained.
At 1420, as the U-Boat appeared to be stopping and not turning so fast to port, the Commanding Officer decided to try to lay the ship alongside and board, in an endeavour to capture some papers at least before she sank. This was rendered impossible by the U-Boat turning sharply to port and ramming Antelope, who was then going full speed astem.
U 31 who had little positive buoyancy, was pushed under and, as the conning tower was open, sank immediately.
Forty-three of the forty-five members of the complement were rescued, two Petty Officers being the only casualties.
See TNA ADM 199/257