HMS Undine attacked a group of German minesweepers off Heligoland on the morning of 7th January 1940 but her torpedoes missed by a matter of feet. With faulty Asdic (Sonar) she was reliant on her periscope to assess the situation, and faulty hydrophones made it difficult to control the submarine. Commander Jackson was finally able file his report on the sinking of his submarine to the Admiralty on 25th June 1945, following release from Prisoner of War camp:
A period of complete quiet followed for about five minutes. Thinking there might be a possibility of attacking again or that the enemy had broken off the hunt, I returned to periscope depth and raised the Low Power Periscope, to look directly at a trawler on the starboard beam, so close that I could see only her port side from the bridge to the aft end of the engine room casing. I immediately ordered “Down periscope, 60 feet”, but before the submarine had really started to go down there were three violent explosions, one aft, one forward and another. (I was informed recently by Leading Telegraph Monserrat that he heard a noise on the port side of the Control Room which sounded like a depth charge scraping the pressure hull, but I have no personal recollection of this.)
The submarine was blown upwards, some lights and glass broken, there was a steady leak in the engine room from near the hatch, a leak in the galley and I was later informed that the Fore End had flooded and had to be abandoned. Both sets of hydroplanes were reported out of action, (the fore hydroplanes hard-a-rise) but the after hydrophones appeared to be working. I ordered “Take her down, flood 0” but the submarine continued to rise until the periscope standards broke surface, giving many of the crew the impression that the drop keel had fallen off.
I therefore raised the Low Power Periscope and saw a trawler bows on on the starboard beam at a range of approximately half a mile. Considering that it was impossible to get the submarine down again to a safe depth before being rammed, I ordered “Surface, burn the C.B.s [Confidential Books], prepare the charge” and went to the bridge, followed by the Leading Signalman who acting on my orders, waved the Negative Flag, which was the best substitute for a white flag available. (Note: Undine was not fitted with a gun.)
Even though the German gunners continued to fire enthusiastically after the flag of surrender had been shown, all the crew were able escape and were rescued from the freezing cold waters. The charges to blow up the submarine failed and the German’s were able to get a man on board the submarine before it sank but he was forced back by escaping gas and smoke, the confidential documents having in any event been destroyed.