Which was the first airship in World War I to be destroyed in mid-air by an airplane?

That the British would take retaliatory measures became evident in April 1915 when Captain Lanoe G. Hawker, of the Royal Flying Corps based at Abeele in Belgium, flying a B.E.2c armed with a few bombs and hand grenades, attacked and destroyed the airship shed at Gontrode, within which, and also destroyed, was LZ38 (LZ38). It was an audacious attack, and highlighted just how vulnerable the airships were when on the ground.

That they might be as vulnerable, given certain conditions, whilst airborne was graphically demonstrated on 6-7 June 1915, when Lt. R.A.J. Warneford Vc, of the RNAS was flying toward Ostend on his first ever night flight. His mission, emulating the earlier effort against Gontrode, was to bomb the Zeppelin sheds at Evere. Whilst en-route he spotted L37 (LZ37) in the clouds. Warneford maneuvered his plane over the vessel and released his bombs, one or more of which hit something solid. In any event there was a great explosion which ignited the gas, and the L37 (LZ37) fell earthwards engulfed in flames. This was the first time an airship had been destroyed by an aircraft whilst in flight.