As per the second pic, it's an Army Parakeet Communications Control Assemblage (CCA). The roof is a pop top to allow 2-3 staff inside.
Parakeet was Army's Battlefield Telecommunications Network. The RAAF were also allocated some equipment. The CCA was the system controlling point at each Parakeet node. From it might hang off Sattelite, Microwave, Optical Fibre or Combat Net Radio Interface communication bearers. It also had other equipment to provide user services internal to the node e.g. to the HQ staff.
Cheers.