Walker joined the Royal Navy as a midshipman in 1908. He served in World War I and saw action during the Zeebrugge Raid in 1918. He became deputy director of Training and Staff Duties at the Admiralty in 1936, commanding officer of the battlecruiser HMS "Hood" in 1938 and commanding officer of the battleship HMS "Barham" in 1939. He also served in World War II becoming Commodore at Portsmouth Dockyard in 1940, Director of Personal Services at the Admiralty in 1941 and Commander of the 5th Cruiser Squadron in 1944. He convened the second and more thorough inquiry into the sinking of HMS Hood, which came to the same conclusion as the first inquiry although other theories have been mooted.