After the war, Castle Williams was used as a military stockade and became the East Coast counterpart to military prisons at Fort Leavenworth, Kansas, and Alcatraz Island, California. Infrastructure and facilities were repaired, unused structures were destroyed, and in 1875 a new munitions warehouse was built north of Fort Columbus. Significant development occurred on the formerly undeveloped northern and eastern sides of the island: the old wood-frame barracks outside Fort Columbus were replaced, and new officers' quarters were built in Nolan Park, east of Fort Columbus. The seawalls on the north and west sides of the island were rehabilitated or extended to create additional buildable land. During this period of expansion, in 1870, a particularly severe yellow fever epidemic occurred on the island, sickening hundreds and requiring a quarantine. The structures that hosted yellow fever patients were later demolished. Despite these changes, in 1873 Fort Columbus and Castle Williams were still described as operable.