Having reestablished the Canadian submarine service, "Grilse" was acquired by the Royal Canadian Navy for use as a training vessel for anti-submarine warfare training on the Pacific coast. However, the boat lacked the speed of more modern subs and her sensor and weapons outfit were not up to the task of anti-submarine warfare. As a result, "Grilse" spent most of her time as "clockwork mice" for surface ships and aircraft, as a passive target for their training. The submarine participated in joint Royal Canadian Navy/Royal Canadian Air Force and joint US/Canada training exercises in the Pacific.