Ion Tiger is an experimental hydrogen-powered fuel cell UAV developed at the Naval Research Laboratory, the corporate laboratory of the Office of Naval Research (ONR). The zero-emission UAV features a 550-watt Polymer Electrolyte Membrane (PEM) fuel cell and high pressure, lightweight hydrogen storage tanks that decrease the vehicle's weight, enabling it to carry up to a six pound payload. The aircraft's electrical motor reduces its acoustic and heat signatures.
From 16-18 April 2013, the aircraft flew for 48 hours and one minute. NRL is working on increasing Ion Tiger's power to 1.5 kW and extending the endurance of the aircraft for up to three days.
2009 NRL video with close ups of prototype aircraft, take-off and landing.