In April 1941, Greenslade was ordered to Mare Island Navy Yard, California, where he assumed duty as commandant of the Twelfth Naval district. While in this capacity, his area of responsibility consisted of the following geographic areas Colorado; Utah; Nevada except Clark County; the northern part of California, including counties of San Luis Obispo, Kings, Tulare, Inyo, and all counties north thereof. Greenslade stirred up controversy, during his service at Mare Island Naval Shipyard, when urged that American-born and alien Japanese be excluded from areas of strategic importance. On April 17, 1942, the Navy seized Treasure Island, San Francisco, California, from the City of San Francisco under the direction of Greenslade, and paid no compensation for the confiscated island. Admiral Greenslade claimed Treasure Island was required for "national security" and appropriated the island for the Navy. On the other hand, Greenslade was very instrumental to the development and wartime growth of Naval Station Treasure Island.
