Able Seaman Cossgrove joined the Auckland Royal Naval Volunteer Reserve prior to WWII. He joined the cruiser HMS NEPTUNE in October 1941. On 19 December 1941, Cossgrove was killed when HMS NEPTUNE was sunk in a minefield off the coast of Tripoli. Of the 750 men on board there was only one survivor. Amongst those lost were 150 Royal New Zealand Navy personnel.