Signal Hill - QE2 procession 1953

Does anyone in the community know something about the building at the foot of Signal Hill (photo from Facebook, taken during a 1953 procession to celebrate the late Queen’s coronation according to a local history group. One member has informed me that this was a British Forces HQ - note the Union Jack and what looks like a regimental flag on the roof, and the onlooking army and navy personnel on the roof and along the entrance/front wall)? Many thanks!