When the Navy F/A-18 jet called the Green Hornet takes off over the Chesapeake Bay on Earth Day, it will aim to break a barrier that has proven far more durable than the speed of sound.

The twin-engine tactical aircraft is prepared on April 22 to make a supersonic flight on biofuel—its tanks filled 50 percent with oil refined from the crushed seeds of the flowering Camelina sativa plant. The test flight at the Naval Air Station at Patuxent River, Maryland will be a milestone in the Navy’s efforts to reduce its reliance on petroleum, and perhaps, in the elusive search for an alternative fuel for aviation.

The event is meant to showcase the Pentagon’s