He was commissioned into the Royal Artillery in July 1943 and later transferred to the Oxfordshire and Buckinghamshire Light Infantry and was posted to the 2nd Ox and Bucks (the 52nd) in September 1944.
Clark was a platoon commander during Operation Varsity: the air assault landing over the River Rhine on 24 March 1945.
The 2nd Ox and Bucks encountered fierce enemy opposition and sustained 50% casualties during the battle of the landing area.
Clark immediately led the remnants of his platoon in a counter-attack with fixed bayonets to recapture the bridge; during the action he also manned anti-tank weapons to stop approaching tanks.
An extract from the citation for his Military Cross reads: " It was entirely due to the determination and rapid action of this officer that a very important bridge was denied falling intact to the enemy.