Warby was the pilot of one of two Lockheed F-5B photo-reconnaissance aircraft (a version of the Lockheed P-38 Lightning fighter) that took off together from Mount Farm on the morning of 12 April 1944, to photograph targets in Germany. Although, as a liaison officer, Warburton should not have been flying operations, and his flight in a P-38 had been opposed by 7th PRG's commander, Lieutenant Colonel George Lawson, it was approved by Lawson's superior Elliot Roosevelt. The aircraft separated approximately north of Munich to carry out their respective tasks; it was planned that they would meet before heading south. Warby was not seen again.