What was the reason for the United States' transition from hydrogen to helium in military airships?

The transition from hydrogen to helium in military airships primarily occurred because helium is far less flammable than hydrogen, which made it a safer option for use in airships. Hydrogen, while providing good lift capabilities, poses a significant fire risk, as evidenced by the catastrophic Hindenburg disaster in 1937. This incident highlighted the dangers associated with hydrogen, including its tendency to ignite easily when mixed with air.

Helium, on the other hand, is a noble gas that does not support combustion. Its use mitigated the risks associated with fire and explosions, making it a more suitable choice for military and commercial airships. This shift prioritized safety in aerial operations, particularly in military contexts, where the risk of loss of life and equipment must be minimized.

While helium does provide good lift—though not as effective as hydrogen in that regard—its primary advantage in the context of military airships was its non-flammable nature. Thus, the key reason for this transition was the need to enhance safety rather than merely improve lift capabilities, reduce costs, or assert abundance.