Plant I's large final assembly building was constructed next to the Red Barn after Boeing was awarded a contract in the late 1910s by the US Navy to build 50 Curtiss HS-2L patrol bombers. The facility was located south of Seattle in the Heath Shipyard on the banks of the Duwamish River. When Plant II was constructed at Boeing Field two miles to the southeast of the facility, the former shipyard became known as Plant I. It was closed in 1970 and sold to the Port of Seattle. The Red Barn was donated to the Pacific Northwest Aviation Historical Foundation and subsequently became the Seattle Museum of Flight's first building.