Project 81 was constructed in 1942 as an Operations and Signals building for the Royal Australian Air Force (RAAF), North East Area Command, in association with the RAAF Base at Garbutt several kilometres to the west. The building survives on Green Street, on the southwest side of Castle Hill in Townsville.

The place comprises two main sections: a large Operations building constructed of reinforced concrete; and a house which was constructed on top as a form of camouflage. Internally, the Operations building has a central corridor running roughly southeast to northwest lengthways, with rooms opening off the corridor. The section remains largely in its original form with only minor alterations. The upper section is a typical timber house, apart from a strong room located in the north-east section of the house.

A concrete fan room still exists to the northwest of the Operations building, and the concrete slab of the former latrines is located near the southwest corner of the Operations building. The former Photographic Intelligence Section building, a low set hut with a combination of a gabled roof and skillion roof disguising the size of its single internal space, is located behind the Operations building and is used as a recreation room by the State Emergency Service (SES). Project 81 was constructed in 1942 as an Operations and Signals building for the Royal Australian Air Force (RAAF), North East Area Command, in association with the RAAF Base at Garbutt several kilometres to the west. The building survives on Green Street, on the southwest side of Castle Hill in Townsville.

The place comprises two main sections: a large Operations building constructed of reinforced concrete; and a house which was constructed on top as a form of camouflage. Internally, the Operations building has a central corridor running roughly southeast to northwest lengthways, with rooms opening off the corridor. The section remains largely in its original form with only minor alterations. The upper section is a typical timber house, apart from a strong room located in the north-east section of the house.

A concrete fan room still exists to the northwest of the Operations building, and the concrete slab of the former latrines is located near the southwest corner of the Operations building. The former Photographic Intelligence Section building, a low set hut with a combination of a gabled roof and skillion roof disguising the size of its single internal space, is located behind the Operations building and is used as a recreation room by the State Emergency Service (SES).