Roberts was put in charge of the ground troops for the raid against Dieppe, on August 19, 1942. His command post was aboard , and due to poor communications he had no idea how his troops were managing, until they called for landing craft for immediate evacuation. Roberts was criticized for unnecessarily committing his reserve troops (Les Fusiliers Mont-Royal) and inadvertently increasing the casualties. He was relieved of his command six months later. It was Roberts's inept performance during a war-game codenamed Operation Spartan in March 1943 rather than the Dieppe raid, which ended Roberts's career. General Harry Crerar reprimanded Roberts for the poor co-ordination between the 2nd Division's artillery and infantry during Operation Spartan war-games, and that Roberts failed to have forces dig in after seizing a bridgehead despite having ample time to do so. After Operation Spartan, Roberts was judged unfit to hold a combat command. He was sent to command reinforcement units in the United Kingdom and received no further operational commands. He later retired to the Channel Islands where he died in 1962.