Walker took command of the 36th Escort Group in October 1941 based at Gladstone Dock, Bootle. The group was led by HMS Stork under his command and comprised the two sloops, Stork and Deptford and seven corvettes, Convolvulus, Gardenia, Marigold, Penstemon, Rhodedendron, Samphire and Vetch. The group operated mainly on the Gibraltar and South Atlantic convoy routes and sank 5 German U-boats.
In June 1942, Walker was promoted to Captain and left the group to take up the appointment ashore of Captain (D) Liverpool and he presented the ensign of HMS Stork to the Former Bootle County Borough Council at a ceremony held in Bootle Town Hall on 1 July 1942.
The 2nd Support Group was formed in April 1943 based at Gladstone Dock, Bootle and was one of five support groups formed to act as reinforcement to convoys under attack, with the capacity to actively hunt and destroy U-boats, rather than be restricted to escort duties. HMS Starling was the flagship of the group under the command of Captain Walker and the other ships of the group were Cygnet, Kite, Wild Goose, Woodpecker, and Wren. The group sank 15 German U-boats under the command of Captain Walker.
On 30 July 1943, the 2nd Support Group encountered a group of three U-boats on the surface while in the Bay of Biscay. Captain Walker signalled "General Chase" to his group and fired at the U-boats, causing damage that prevented them from diving. Two of the U-boats were then sunk by the Support Group and the third by an Australian flying boat. “General Chase” is signalled to release ships from a line of battle, or other formation, in order to pursue a retreating or beaten foe. The signal is appropriate to the end of an action, when victory is certain and it allows all ships to break formation and act independently in order to pursue at best speed to capture or destroy enemy vessels. The ‘General Chase’ signal had only been used twice before in the Royal Navy – once by Sir Francis Drake, when he chased the Spanish Armada from the Channel in 1588, and again by Rear Admiral Horatio Nelson when he defeated Napoleon’s fleet at the Battle of the Nile in 1798.
Soon after the 2nd Support Group was formed in 1943, HMS Starling was adopted by the Former Bootle County Borough Council because Gladstone Dock was within its boundaries and the Captain (D) Liverpool made arrangements for the “General Chase” signal flags which Walker had used in the Bay of Biscay to be handed over to the Council at a ceremony held in Bootle Town Hall on 5 January 1944 which was attended by Captain Walker and his wife, Eilleen.
Captain Walker suffered a cerebral thrombosis and died on 9 July 1944 at the Naval Hospital at Seaforth aged 48 and his death was attributed to overwork and exhaustion. His funeral service took place at the Liverpool Anglican Cathedral with full naval honours and attended by about 1,000 people. The naval procession took place through the streets of Liverpool to the docks, where his body was embarked aboard the destroyer HMS Hesperus for his final journey to be buried at sea in Liverpool Bay.
After the war, Admiral Sir Max Horton, Commander - in - Chief Western Approaches, considered that victory in the Atlantic was due more to Captain Walker than to any other individual and commented that “Victory has been won, and should be won, by such as he.”
The final voyage of HMS Starling was a call to Bootle to attend a farewell celebration provided by the Council and Captain Walker’s widow took passage in Starling’s final sailing from Bootle to Portsmouth in 1956.