Convoy ONS 5 was to come into contact with 40 U-boats in total. In earlier times this might well have turned into a catastrophe. As it was 13 out of 42 merchant ships were sunk. But the 16 escort ships proved to be adept at fighting back. The tactics for taking on U boats were now well developed and improvements to the radar and asdic had been matched with increased firepower, notably with the Hedgehog mortar, which threw a pattern of small charges rather than one large depth charge.
Some idea of what that meant for the ships involved can be gained from the log of HMS Snowflake, which was almost continuously in action for several days. By the early hours of 6th May she was already recording the 10th separate attack on a U-boat. There was a tension between making an attack on a U-boat and staying with the convoy to provide protection. In such circumstances the delay caused by stopping to pick up survivors from a U-boat would not always be approved:
INCIDENT SNOW 10 . 6th May 1943.
0022 Obtained R.D.F. contact bearing 090 degrees 4000 yds. Altered course towards and commenced chase illuminating target with starshell alternatively firing H.E. Reported to TAY, U-boat 3 o’clock 5 miles.
0030 U-boat dived on course 090 degrees range 600 yds.
0031 Fired heavy charges from port and starboard throwers set to 140 ft.
0032 Regained contact astern. Opened range to 1000 yds. Turned for second run in to ascertain whether U-boat had gone deep.
0035 Passed over U-boat, contact being held to “instantaneous echoes”.
0036 Regained contact astern, ran out to 500 yds.
0038 Carried out second attack, with one heavy charge set to 140 ft. in an endeavour to persuade the U-boat to stay down.
0039 Contact regained astern but I had insufficient time or charges to attack. Set course to rejoin.
0100 In station R.
INCIDENT SNOW 11. 6th May 1943.
0130 R.D.F. contact bearing 030 degrees, range 4100 yds. Reported U-boat to TAY 8 o’clock 5 miles. Chase commenced on course 055 degrees range slowly being reduced. By this time fog had closed in and starshell were useless. 4″ H.E. was being fired directly by R.D.F.
0136 U-boat endeavouring to work to the Southward.
0138 U-boat on course 115 degrees.
0140 U-boat dived bearing 125 degrees range 400 yards.
0141 Ran over U-boat dropping one heavy charge set to 140 ft. R.D.F. contact obtained of second U-boat bearing 170 degrees range 2400 yds.
0141-1/2 Altered course to 170 degrees and reported second U-boat.
0142-1/2 U-boat moving very rapidly left. Altered course to 130 degrees to intercept. Enemy being engaged with H.E.
0145 U-boat dived. Obtained R.D.F. contact of third U-boat bearing 185 degrees 1000 yds. Broke off attack on second U-boat through risk of torpedo attack from third. Altered course to 160 degrees. Reported to TAY.
0146 U-boat dived.
0147 Asdic contact bearing 160 degrees 700 yds. Ran in to attack with last charge.
0149 SUNFLOWER ordered to my assistance.
0150 Lost contact by Asdics. Reported situation to TAY charge not dropped.
0151 Altered course to port to 300 degrees, to carry out R.D.F. sweep through the last known area of three U-boats with the object of ascertaining whether any of the U-boats had surfaced.
0154 R.D.F. contact bearing 250 degrees 3200 yds. Altered course towards. R.D.F. reported that the U-boat appeared to be low in the water. The speed at which I closed indicated that the U-boat was stopped.
0159 Range had closed to 500 yds. and bearing commenced to move right. Course altered 10 degrees to starboard. Gained contact with Asdic.
0200 Range had closed to 100 yds. Starboard searchlight switched on revealing a 500 ton U-boat swinging rapidly to starboard. Wheel was put hard-a-starboard in an attempt to ram and all guns that would bear opened fire. Ship turned inside the U-boat’s turning circle and came up alongside her starboard side with only a few feet separating the two. By this time the enemy was being illuminated by port searchlight and 10″ S.P. and was seen to be in a sinking condition. The conning tower was buckled, periscope standards twisted, A.A. gun wrecked, casing in way of the after hatch torn away and the lid of the after hatch appeared to have been blown away. Guns could not be depressed sufficiently to hit. As the ships drew apart the stern of the U-boat settled with constant streams of air bubbles rising from the water hatch. Crew were seen to be abandoning ship but an attempt was made to man the forward gun, this attempt was defeated by accurate shooting from the 2Pdr. and port Oerlikon plus some intimidation from the 4″ which missed. Some of the crew waved their arms, presumably as a signal to cease fire, this was ignored.
A report was made that the U-boat had been sunk by ramming as I was under the impression that the port bilge keel had torn a hole in the U-boat’s starboard side. This was subsequently found to be wrong.
0211 R.D.F. Contact obtained bearing 160 degrees 1400 yds. Reported as U-boat fully blown. Set course to ram being the only means left to deal with U-boats.
0213 Searchlight switched on revealing SUNFLOWER. Wheel put hard-a-port and collision successfully averted.
0214 U-boat’s scuttling charges heard to explode. The first was louder than the following four.
Swept back through area illuminating survivors swimming in oil and some in a small dinghy.
As SUNFLOWER was with me I requested permission to pick up a few prisoners for interrogation. This was not approved. Course set to rejoin.
0218 Asdic contact obtained bearing 130 degrees 1600 yds. Altered course to investigate reporting to SUNFLOWER.
0221 Lost contact.
0226 Set course to resume station.
0318 In station.
INCIDENT SNOW 12 . 6th May 1943.
0402 SNOWFLAKE in position R LOOSESTRIFE reports U-boats coming towards me. Altered course to intercept.
0406 Sighted LOOSESTRIFE in the half light of dawn steering about 045 degrees. U-boat had apparently altered course to the Northward. In the meantime course was altered to 060 degrees and R.D.F. ordered to sweep ahead of LOOSESTRIFE.
0412 R.D.F. contact obtained bearing 047 degrees 3000 yds.
0413 Opened fire with starshell but illumination was damped by slight mist, chase continued range being slowly reduced H.E. being fired directed by R.D.F.
0416 Asdic in contact by hydrophone effect.
0417 Very loud whistle effect heard lasting 5-10 seconds.
0418 Two torpedoes passed down the port side, not heard by Asdic. The whistle effect was considered to have been caused by the U-boat regaining trim after firing torpedoes.
0421 U-boats dived. Told LOOSESTRIFE to carry on and that I would act as directing ship. Altered course to 150 degrees and assumed the duties of directing vessel.
0430 LOOSESTRIFE attacked. Contact lost after this attack.
0433 Set course to resume station.
0500 Dense fog. Convoy scattered. Rounding up stragglers.
The original reports and those for the other ships involved in escorting ONS5 can be found at U boat Archive.
HMS Snowflake had finished off U-125, which had earlier been damaged by ramming by HMS Oribi. Other U-boats had been ordered to go to her aid at the time she was attacked by HMS Snowflake. Her commander and 54 crew were not picked up and all were lost.
In total the ONS 5 convoy escort succeeded in sinking six U-boats, and seriously damaging seven more that had to return to port immediately. It was the beginning of ‘Black May’ for the U-Boat crews. The tide had turned in the Allies favour in the Battle of the Atlantic.