Sergeant Cassidy was wounded 14 July 1943 during operations at Agnone, Sicily, and the bridge at Malati (3 Commando Bridge). He was initially attested into the Royal Artillery before the war until discharged 11 March 1938. He then joined the Metropolitan Police and in 1939 was a Constable at Hornsey. Re-enlisted Royal Fusiliers 9 June 1942 after volunteering for the Commandos. The 1st Police Intake at the Commando Basic Training Centre, Achnacarry, commenced later that month.