The Second Battle of Fort Defiance was a military engagement fought during the United States period of the Navajo Wars. On August 30, 1860, about 1,000 Navajo warriors assaulted the United States Army garrison of Fort Defiance in New Mexico Territory, now within present day Arizona. The Navajo achieved a surprise attack but was ultimately repulsed by 150 American defenders of the 3rd Infantry under Captain Oliver L. Shepherd.