'Protonex said the military version of the UAV-H500 was used by the U.S. Naval Research Laboratory to set a flight endurance record on its small, unmanned aerial vehicle, the Ion Tiger. The aircraft was aloft for more than 26 hours, setting an endurance record for fuel cell powered flight.'
Another model of Fuel Cell using Liquid Hydrogen sets a new record this spring - 48 hours of flight time. A project sponsored by the Navy.