The U.S. military has named the Air Force fighter jet pilot killed Monday in a training accident off the coast of England. The U.S. Air Force 48th Figher Wing said Tuesday that 1st Lt. Kenneth Allen, assistant chief of weapons and tactics for the 493rd Fighter Squadron, was killed when his F-15C Eagle crashed into the North Sea for reasons which remain unclear.

Allan had been based with the 48th Fighter Wing at Royal Air Force Base Lakenheath, in eastern England, since February. 

“We are deeply saddened by the loss of Lt. Allen, and mourn with his family and his fellow Reapers in the 493rd Fighter Squadron. The tremendous outpouring of love and support from our communities has been a ray of light in this time of darkness,” Colonel Will Marshall, 48th Fighter Wing commander, said in the statement released Tuesday. Allen is survived by his wife and parents.

Allen’s wife Hannah, who called him “Kage,” posted a tribute to her husband on  her Facebook page Tuesday, according to U.K. news outlets. She said there were “no words to express how shaken I am.” 

“He was my absolute best friend and man Christ needs hurry up and come back so I can be with Kage again,” she said. “I feel beyond blessed to have loved him in this life and can’t wait to love him for eternity. #youaremyforever.”

It took search and rescue crews hours to find Allen after the crash on Monday. The jet, deployed from RAF Lakenheath, crashed at about 4:40 a.m. Eastern. 

“At the time of the accident, the aircraft was on a routine training mission with one pilot on board,” the 48th Fighter Wing said in a brief statement Monday, adding that the cause of the crash remained unclear.

BBC News quoted a spokesperson with the U.K. Coastguard as saying one helicopter and two lifeboats joined the initial search for the downed aircraft, about 90 miles off the coast of northeast Yorkshire.  

Hours before the crash, RAF Lakenheath posted a photo to the base’s twitter account showing F-15s in flight, saying the 48th Fighter Wing was ready to “take on Monday.”

The U.S. 48th Fighter Wing has been based at RAF Lakenheath since 1960. It currently boasts a force of about 4,500 service members. The single-seat F-15C has been used by the U.S. Air Force for more than 40 years, and more than 200 remain in active service.