With the outbreak of the Second World War, Clement was commissioned into the 4th Battalion of the Welsh Regiment. He was injured in action twice, the first time was during the Battle for Caen, during the action for which he was awarded the Military Cross (MC). On 23 July 1944, Clement, now a war substantive captain and temporary major, was part of a raid on enemy positions around Le Bon Repos, near Caen. Clement was in command of one of two companies of the Welch Regiment involved in the operation, but as they advanced down a 900-yard slope toward the objective, he and his men came under heavy fire and Clement was injured in his leg. They suffered high levels of casualties, one of Clement's platoons was all but wiped out, with just four survivors. Casualties with this platoon included one of just two other officers who had started the attack with Clement. He managed to rally his troops and engaged the enemy in close-quarter combat, killing at least 30. When ordered to withdraw, Clement remained until his wounded had been recovered, and only then returned to the rendezvous, where he finally agreed to receive medical treatment. For his actions in this encounter he was awarded the Military Cross on 21 December 1944. In 1945 he was wounded in action in the Netherlands, again while in charge of his company of the 4th Battalion.