The first mission systems-equipped Lockheed Martin [NYSE: LMT] F-35 Lightning II test jet joined the fleet at Naval Air Station Patuxent River, Md., today.

Piloted by F-35 Test Pilot Dave "Doc" Nelson, the short takeoff/vertical landing (STOVL) F-35B known as BF-4 became the fourth F-35 to arrive and begin testing at the Naval Air Systems Command site. The STOVL variant will be employed by the U.S. Marine Corps, the U.K. Royal Air Force and Royal Navy, and the Italian Air Force and Navy.

"This mission systems aircraft adds a new dimension to the F-35 flight testing under way at PAX River," said Tom Burbage, Lockheed Martin executive vice president and general manager of F-35 Program Integration. "Now, in addition to validating the aerodynamic capabilities and flying qualities of these jets, we will have the opportunity to confirm the performance of what we expect to be a transcendent avionics capability – the most capable ever in a fighter." A fifth F-35B, along with the first Navy carrier variant, is expected to join the fleet later this year at Patuxent River.

The F-35's avionics, or mission systems, enable the jet to perform a wide variety of missions by providing the pilot with unprecedented situational awareness – through the processing and fusion of data from both on-board and off-board sources. The F-35's next-generation sensor suite makes it possible to collect vast amounts of information, and present the data on state-of-the-art cockpit and helmet displays. This allows the pilot to make faster and more effective tactical decisions and transfer information to other aircraft and to maritime and ground forces.