the young pierre spent two years in the colonial regular troops las a cadet, doing garrison duty in montreal. in 1731, when his father planned an expedition to expand the fur trade westward and at the same time search for a water route to the western sea, he accompanied his father and brothers jean baptiste, françois, and louis-joseph as a member of the expedition. he spent the winter at fort kaministiquia while his older brother jean baptiste and his cousin and the second in command, christopher dufrost de la jemeraye, carried on to rainy lake and established fort st. pierre. in 1732 he accompanied his father to lake of the woods, where they built fort st. charles.