The aircraft, one of three Britain is buying from the United States under its Airseeker program, was flown at RAF Waddington in Lincolnshire, the ministry said, but details of that first RAF flight were not provided.
The RC-135W is a converted Boeing KC-135 tanker. The conversion was conducted by L-3IS in Greenville, Texas. Britain is buying the three aircraft from the U.S. government for about $1 billion.
"The first flight of the UK's Rivet Joint RC-135W aircraft, as part of the Airseeker program with an RAF crew, is a proud moment for all in the Defense Equipment and Support team who have worked, and continue to work, so hard to deliver this outstanding capability to the front line," said the MOD's Chief of Materiel, Air Marshal Simon Bollom.
"We have procured an aircraft with a proven track record which has been successfully operated by the United States Air Force, with RAF crews under co-manning arrangements, for a number of years.
"We have worked very closely with our colleagues in the US on this project and today's (Tuesday) first flight signifies the commencement of a new and potent air ISTAR (intelligence, surveillance, target acquisition and reconnaissance) capability in the RAF inventory," he said.
The aircraft will provide Britain with real-time signals intelligence and surveillance capability through advanced sensor technology. Analysis of that information can be carried out on board the aircraft and disseminated from it.