While rejoining screen after an unsuccessful search from an aircraft sighting report, tapping noises were heard on the Starboard side.  Course was altered to investigate and contact was gained at 1800 yards, probably on the U-boat's wake.  The tapping noise is thought from information obtained from prisoners, to have been from a pump which was running at the time. 

        Acoustic conditions were excellent, and no Non-sub echoes were obtained.

        U-boat, by plot, appeared to steam away in the early stage of the attack followed by a tight turn.

        I considered that as the U-boat must have been in a position to attack the Convoy and had not done so, that she must be well below periscope depth and was hoping to avoid detection before surfacing astern and shadowing.  For this reason I used Pattern "E" (150' and 300') which appears to have been a lucky guess.

        During second attack I was committed to a Hedgehog attack when contact faded at 450 yards.  I consider U-boat was deep, and with closing speed of only 5 knots, I did not expect success.  Echo Sounder was used, but gave no results.

        I opened range and regained contact at 750 yards and turned to attack with deep settings.  While running in bows of submarine surfaced at a steep angle, about three cables ahead, submarine leveled off and I was in ideal position to ram.  As convoy was known to be shadowed, and I was far from home, I decided to engage with gunfire and altered to a parallel course, reducing to slow.

        At least three hits from 3" guns were seen at base of Conning Tower, and other on the water line, whilst close range weapons prevented U-boat from manning her guns.  From observation and prisoners' statements, it is not thought that any 3" penetrated the Conning Tower or Pressure Hull.

        When it was obvious that U-boat was sinking and crew abandoning ship I ceased fire and proceeded to pick up survivors.  One officer, five N.C.O.s and twenty-one others were picked up.  Light was failing and remainder of those seen in the water appeared to have drowned.  Course was set to regain position on the screen.

        U-boat was U-841 and of 750 ton type.  Breaking of cell containers of Main Battery, and leakage of water caused by Depth Charges, are believed to have been cause of U-boat surfacing.

                                                                                                    File No. S.1048-48-20

                                                                                                    F.D.       ONS 20 (Staff)

If the U-841 Final Report is not yet complete you may care to have D.W.T's Appreciation of the sinking of this U-boat by H.M.S. "BYARD".

H.M.S. "BYARD"  -  1895Z/17

        While returning to station after an unsuccessful search, tapping noises were heard on starboard side.  Asdic contact was subsequently made, and a depth charge attack commenced.  The C.O. reasoned that since the U-boat must have been in a position to attack the convoy, and had not done so, he must be well below periscope depth and was hoping to avoid detection before surfacing astern and shadowing.  He accordingly used a deep setting, which later proved to have been the correct one.  This attack was followed by a hedgehog attack which did not result in any explosions, and while turning to attack the third time, the U-boat surfaced at a steep angle.  This offered very strong temptations to ram, but since convoy was known to be shadowed and since the position of the attack was far from the nearest base, the C.O. reasoned that it would be better to engage with gunfire.  Several hits were observed before the U-boat commenced to sink.  One officer, 5 N.C.O.'s and 21 ratings were picked up.

        The Commanding Officer of H.M.S. "BYARD" is considered to have used excellent judgment in carrying out this attack.

                                                                                            D.W.T./TACTICS.

OTTAWA

23 December, 1943.