The cause of a fire in a regimental headquarters at Palace Barracks in Holywood has not yet been established, the fire service has said.
NI Fire and Rescue personnel were called to the sprawling Co Down base, which is also the home to MI5 in Northern Ireland, around 7.15am on Wednesday.
The blaze broke out on the first floor of the Royal Irish Regiment headquarters destroying a number of historic artefacts.
Regimental secretary Major Colin Gray told Forces Radio BFBS that no one was injured and that a number of more valuable pieces of memorabilia have been saved – including two important statuettes and a cigar box.
“We are very lucky that the fire started at one end of the building...the end of the building that had less of our valuable artefacts and history in it,” Major Gray said.
“The other end of the building where the really valuable regimental memorabilia is isn’t quite as badly damaged.”
Major Gray said no one had been injured as a result of the blaze.
“Thankfully the fire started before we got into work this morning, it’s only property that’s been damaged.”
Much of the building’s roof has been destroyed.
A NIFRS spokesman said the cause of the blaze was “undetermined,” at this stage, but that further investigations could take place when the building has been made safe.