In June 1940, the U.S. Congress passed Public Law 635, known as the “10,000 Plane Program,” in response to the escalating war in Europe. One of the goals of that initiative was to expand the nation’s lighter-than-air (LTA) program by constructing new coastal facilities and 48 non-rigid airships, or blimps, that would be used for submarine surveillance operations. The attack on Pearl Harbor on December 7, 1941, redefined and accelerated those initial plans.

New LTA hangars were originally going to be made with steel. The Second Deficiency Appropriation Bill for 1941 regulated the use of strategic materials, and the Navy determined that most metal would be utilized for its ambitious wartime shipbuilding and weapons production efforts. As a result, the Department of the Navy Bureau of Yards and Docks designed and engineered a standardized set of ingenious plans for the world’s largest freestanding wood-frame structures. Between 1942 and 1943, 17 nearly identical timber and concrete hangars were built at ten different U.S. Naval bases. Each enormous building was large enough to house a squadron of six to ten blimps, depending on their type.

Control of Moffett Field was transferred from the U.S. Army back to the Navy in 1941, and the site became dedicated to training the LTA pilots and crews that patrolled the coastlines of California, Oregon, Washington, Hawaii, and Alaska. Two wood hangars were rapidly constructed so that they could be used by the Navy Station Assembly and Repair Department to assemble, store, and maintain the blimps and untethered “free balloons” that were a critical part of the LTA pilots’ aviation exercises.

Hangar 2 and Hangar 3 were built on the east side of the airfield in a side-by-side configuration that was on axis with and parallel to Hangar 1, located on the opposite side of the runways. The construction of Hangar 2 began on August 22, 1942. It was completed in 372 days and cost approximately $2.5 million. The Hangar 3 project started on November 3, 1942. It was built in 208 days at an expense of about $1.8 million. Both structures were finished in 1943, thanks to an efficient production process that included the onsite assembly of prefabricated trusses.

The 121-foot-tall doors on the north and south ends of each building were supported by a single 200-foot-long wood box beam resting on two cast-in-place concrete towers. The 147-foot-tall towers were structurally separate from the hangar’s timber truss system, in order to resist gravity and wind loads. A total of 816 concrete piles were used for the foundations of the hangar’s four towers. An interior ladder provided access to each tower’s eight internal platform levels.

The enormous entryways were crowned with clamshell domes that enclosed the space between the horizontal beam and the hangar’s curved roof line. The door assembly included six aluminum and wood frame sliding panels, each weighing 26 to 29 tons, that moved along a series of guide rails embedded in the concrete slab floor. To minimize the negative effects of unpredictable winds, the overlapping door system did not extend beyond the profile of the hangar.

The two-foot-three-inch thick foundation slab was made of 20-by-20-foot panels of poured-in-place and reinforced concrete separated by one-inch expansion joints. Rail tracks installed in the floors of Hangars 2 and 3 helped a small car with a mooring mast pull the blimps to safety from the circular landing pads located to the north and south of the buildings. A regular pattern of metal rings, called blimp tie-downs, was also attached to the concrete slab.

Improvements and Repairs

The development of Hangar 2 and Hangar 3 was part of the Navy’s Accelerated Public Works Program. Their expedited production schedule, due to World War II, prevented rigorous research and testing from being executed. The lack of in-depth analysis and detailed strategies for an innovative timber project of such an immense scale resulted in numerous issues during the project’s design and construction.

In 1945, a two-story annex that was 60 feet wide and 1,000 feet long was built on the east side of Hangar 3, in order to provide additional support and service areas. In 1956, the original tarpaper rolled roofing on each hangar was replaced with 466,000 square feet of green corrugated aluminum panels over straight wood sheathing. In 1946, just three years after the hangars were completed, an extensive remediation project was implemented to strengthen the trusses throughout each building. Wood battens were added to structural members to increase stability and prevent buckling. Timber knee-braces were also added to reduce the unbraced length of vertical web members. In the decades that followed, steel clamps, stitch bolts, glulam members, and steel pipe shores were added to Hangar 3, in an ongoing effort to stabilize the failing structure and prolong its lifespan.