During the time of Palpatine's Galactic Empire, the Imperial Army relied largely on Stormtroopers for it's legions of ground troops. However, with the rise of the Rebel Alliance, sometimes the Empire's Army was forced to loan out Imperial Navy troopers from the Imperial Navy for temporary (more-or-less) use as foot soldiers in case the Imperial Army was short on Stormtroopers. This policy continued under the Imperial Remnant.