10/20/2026
It was an aluminum blimp, not a lead balloon.
For this week's , we look at the U.S. Navy’s USS ZMC-2. An aircraft unique in the history of airships for having a rigid metal skin instead of a fabric envelope.
Built to test the idea that a practical airship be constructed with a metal hull, the short, broad, and bulbous experimental craft was approximately 149 feet long and enclosed about 200,000 cubic feet of helium. Its defining feature was its metal skin. Instead of the fabric envelope used by blimps or the fabric-covered framework and internal gas cells of a Zeppelin, the ZMC-2 used an extremely thin aluminum alloy covering that served both as the gas container and as part of the load-bearing structure. The skin was about 0.0095 inch thick and was joined with roughly 3.5 million tiny rivets.
Two Wright J-5 Whirlwind radial engines mounted on outriggers beside the control car provided power, giving the airship a cruising speed of about 50 mph and a maximum speed slightly above 60 mph.
The idea grew from the work of balloonist and engineer Ralph Hazlett Upson and the Aircraft Development Corporation of Detroit. Conventional rigid airships required an elaborate framework, separate gas cells, rigging, and an exterior fabric covering, all of which added weight and maintenance. A thin metal shell promised to combine several of those functions while also resisting weather deterioration far better than fabric. Building such a hull was difficult because every seam had to be both structurally sound and virtually gas-tight.
The ZMC-2 was therefore constructed in two halves, each suspended vertically while successive strips of metal were added. A special automatic riveting machine moved around circular tracks and installed the minute rivets in closely spaced rows. Although early construction involved duralumin, the hull covering became an important early application of Alcoa's Alclad, which combined a strong aluminum alloy core with corrosion-resistant pure aluminum surface layers.
ZMC-2 made its first flight at Grosse Ile, Michigan, on August 19, 1929. The flight lasted just under 50 minutes, and the early trials went remarkably well. Contemporary reporting stated that every test required by the Navy contract was completed on the first attempt without alterations to the airship, an impressive result for something based on such an unconventional construction method. After further testing it was flown nonstop from Michigan to Naval Air Station Lakehurst, New Jersey, where the Navy subjected it to prolonged experimental and training service.
The strange little ship ultimately proved far more durable than skeptics might have expected. By its sixth anniversary it had flown more than 57,000 miles and accumulated over 1,400 flight hours, and by the end of its career it had exceeded 2,200 hours. Its metal hull remained in good condition and remarkably gas-tight. The experiment therefore did not fail in the ordinary sense. What failed was the economic and operational case for building more of them. The metal-clad design showed no overwhelming advantage over conventional airships, the Great Depression badly damaged financing for further development, and enthusiasm for large airships declined as conventional aircraft became steadily more capable. The Navy commissioned engineering studies for larger metal-clad ships in 1932, but none was built.
For an experimental aircraft that never entered production, the ZMC-2 enjoyed an extraordinarily long afterlife. Instead of being discarded after a few test flights, it served the Navy for approximately twelve years, mostly at Lakehurst, providing both operational experience and long-term information about metal hull construction.
Its handling could be troublesome in rough air and at low speeds, although Navy historians attributed much of that behavior to the ship's unusually small size rather than to the metal-clad principle itself. More importantly, repeated inspection demonstrated that its thin metal envelope could survive years of vibration, pressure changes, handling, and exposure without the catastrophic cracking or leakage that critics had feared. Yet no ZMC-3 followed.
With the United States moving toward large numbers of cheaper non-rigid patrol blimps and heavier-than-air aircraft, there was little incentive to resurrect an expensive technology whose greatest advantages would probably have appeared only in much larger ships. ZMC-2 was finally stricken and scrapped in 1941, its still-serviceable hull sacrificed as the Navy expanded for war. No prototype survives today.
