the cruiser , who initially tried to direct Walkers ships into a tight screen, but soon allowed him to independently command the two support groups from Western Command. Walker's own ship Starling sank the on 29 March, the group's first day with the convoy, and subsequently the ships under his command sank and before they arrived at Murmansk without the loss of a single ship. The groups returned with the 36-ship convoy RA 58, but despite intelligence of 16 U-boats in their path, no contacts were made due to adverse conditions affecting the ASDIC (sonar). Walker's last duty was protecting the fleet from U-boats during the Normandy landings, the immense Allied invasion of France. This he did successfully for two weeks; no U-boats managed to get past Walker and his vessels, and many U-boats were sunk or damaged in the process. During this concerted effort Walker's dedication to his tasks was tremendous; he took no respite from his duties, which ultimately contributed to his death. He was awarded the third bar on his DSO on 13 June 1944, and was again Mentioned in Despatches on 20 June 1944. Methods One highly successful tactic employed by Walker was the creeping attack, in which two ships would work together to keep contact with a U–boat while attacking. A refinement of this was the barrage attack, in which three or more sloops in line to launch depth charges to saturate the area with depth charges in a manner similar to a rolling barrage by artillery in advance of an infantry attack. Walker was also adept at, once having contact with a U-boat, keeping it at depth below depth charge detonation range, until it needed to surface due to running out of air or battery, and then defeating it. Successes Walker was the most successful anti-submarine commander of the Second World War, being credited with 17 U boats destroyed, from various ships. Death Walker suffered a cerebral thrombosis on 7 July 1944, and he died two days later at the Naval Hospital at Seaforth, Merseyside, at the age of 48. His death was attributed to overwork and exhaustion. His funeral service took place at the Liverpool Anglican Cathedral with full naval honours, being attended by about 1,000 people. A naval procession followed escorting the body through the streets of the city to the docks, where it was embarked aboard the destroyer , for a