"Peterson could only be in one of two places at this stage in his life. In France, engaging enemy combatants, or doing hard time in prison back home."
— Call of Duty 3 bonus materials section.
He took part in the Battle of the Falaise Gap in France in 1944. His commander was Robiechauld. When Robiechauld says to his men "A glorious victory or a glorious death awaits." Peterson asks, "Do we get to pick which one?". Private Baron then says, "Show the lieutenant some respect!". Peterson responds by saying, "Who's this pissant?".
He is seen in every Canadian campaign level, though, he usually only has a minor role. He seems to have a good relationship with Cole and Sgt. Callard. He does not appear in the first half of the level "Corridor of Death" and he was rendezvous with Lt. Robiechauld after the player is told to take out a set of Machine Guns.