China ? A window has opened for families of the 8,100 American servicemen missing since the Korean War, with China agreeing on Friday to allow access to sensitive military records – but only to Chinese researchers at first.

Families of missing servicemen were excited by Friday’s military archives agreement, one the U.S. government has long requested. Chinese troops killed and captured thousands of American troops during the Korean War and managed many of the prisoner of war camps set up in North Korea during the war.

“I think this is a fantastic opportunity if the Chinese are serious about divulging all the information to us,” said John Zimmerlee, founder of the Korean War POW/MIA Network for families of missing servicemen.

In another sign of warming U.S.-China military ties, the two countries also agreed to set up a military hot line for communicating in emergencies, a step long sought by the U.S. to build trust and transparency in their relations.