This is a World War 2 AA mount for a light AA gun on the South end of the RML Gun emplacement.
This has been identified as a mounting position for a single launcher for an Unguided Projectile, UP. These rockets, were generally known as Z Batteries and a reasonable number of these AA gun positions, installed during WWII, survive in Gibraltar and are rare. It is assumed that the ammunition, rockets, would have been stored immediately to the rear of the launch position,
Identification of this position based on Rollos work and the metal tie downs still in place.