Hangar One, Military hangar at Moffett Federal Airfield, United States

Hangar One is a military hangar at Moffett Federal Airfield in Santa Clara County, measuring 1133 feet (345 meters) in length and 308 feet (94 meters) in width, among the largest freestanding buildings in California. The steel framework was designed to house massive airships and features a curved roof extending across the entire span.

Built in the early 1930s as a naval airship hangar for USS Macon, Hangar One was designed by Karl Arnstein of the Goodyear Zeppelin Corporation with Wilbur Watson Associates. Macon, 785 feet long, was based at Moffett only briefly before its 1935 crash. The hangar was listed on the National Register of Historic Places in 1994 and named one of America's 11 Most Endangered Historic Places in 2008. Google subsidiary Planetary Ventures took over management in 2014, and restoration was reported complete in December 2025.

The hangar's nickname comes from its Navy designation, Hangar Number One, and locals have called it that since the airship years. It appears in the 1934 film Here Comes the Navy, shot while USS Macon was based at Moffett Field. The building is a landmark of Silicon Valley, and its 2008 listing among America's 11 Most Endangered Historic Places drew public support for keeping it standing.

Hangar One stands on Moffett Federal Airfield, an active federal site, so the grounds are closed to the public; the structure is seen from outside. The long axis runs roughly northwest to southeast, and the arched lattice shell is visible from public roads around the airfield perimeter. The twelve rows of small windows on the ribbed grey wall and the star on the dome are best picked out from a distance, where the whole profile fits in view.

The interior space is so large that fog can form near the ceiling under certain temperature conditions, a phenomenon seen in only a few buildings worldwide. The massive clamshell doors each weigh around 200 tons and were designed to minimize wind turbulence when airships moved in and out.