. >> reporter: when admiral paul halsey made a triumphant return after world war ii, it was perhaps the most climatic fleet week in history. the history of the military in the bay area started long before that. when the spanish wandered into the bay and instantly realize its value. >> it was decided to establish a a permanent army post in 1776. >> they called it l presidio day day san francisco. with the milewide goldengate of being the the only opening to the bay, it made for a perfect military situation. >> they put cannons on both sides of the entrance, so that back guys that tried to sale and and would be caught in the crossfire. you control the entrance to the goldengate, you control the harbor. >> reporter: the territory passed from spain, to mexico, to to the united states. in 1949 everything changed. gold was discovered. >> the explosion in economics and people brought by gold, that that is what led to the u.s. government saying that we have to defend this. >> reporter: the presidio was expanded. by the civil war, at e western end of the bridge, was a a large brick fortress that