Alexander Johnson was born in Portsmouth, Hampshire, on 16 April 1902, the son of James George and Alice May Johnson. He joined the Royal Navy as a Boy Artificer on 28 July 1917. He completed his apprenticeship on 5 January 1922 and then served in the battleship HMS RAMILLIES, the Destroyer Depot Ships HMS DILIGENCE and HMS SANDHURST, the destroyers HMS VETERAN and HMS WITHERINGTON until 1 February 1926. This was followed by HMS DOLPHIN, HMS CONQUEST, HMS REVENGE and HMS WITHERINGTON.

Engine Room Artificer Second Class Alexander Johnson joined submarines at HMS DOLPHIN on 20 October 1933 for the Submarine Course and HMS H44 on 27 March 1933 until June 1935. After drafts to HMS DOLPHIN, HMS MAIDSTONE, and HMS CYCLOPS he served in HMS OSIRIS, HMS PORPOISE and then HMS NARWHAL until 12 January 1939.

After the outbreak of war, Chief Engine Room Artificer Alexander Johnson was drafted to HMS TAKU on 1 October 1939. He was awarded the DSM – see London Gazette dated 28 June 1940. He was promoted to Acting Warrant Engineer on 1 April 1941 and was appointed to the Submarine Depot Ship HMS MEDWAY at Alexandria on 10 September 1941.

Alexander Johnson was then appointed to HMS PERSEUS as Engineering Officer. PERSEUS was ordered to conduct a patrol off Eastern Greece and is reported to have struck a mine in the late evening of 6 December 1941, off the island of Cephalonia and then to have settled on the bottom. There was only one survivor who managed to escape from the after ends of the boat. Alexander Johnson was the husband of Dorothy Elinor Johnson (née Dickson), and is commemorated on the Portsmouth Naval Memorial on Panel No.46 Column No.1.