During World War II radar was a most secret technology. It had been developed in Britain prior to the war and the details were shared with Australia and other commonwealth countries. Delays in acquiring British radar equipment, due to the demands of the Battle of Britain, spurred an innovative period of radar development by Australian scientists at the Radiophysics Laboratory (RPL) of the University of Sydney during 1941.

It was fortunate that as the war with Japan approached, there were in Sydney two very important manufacturers with the expertise to produce specialised radar equipment, namely HMV (His Master’s Voice), also known as the Gramophone Company, and the New South Wales Government Railway Workshop. These two organisations were capable of providing the Australian air warning (AW) equipment, particularly the RPL-designed transmitter/receivers and aerials. However, in September 1941 it was apparent it would take at least a year for construction of the local sets required for each of the planned 32 ground stations around the country, including Cooktown. The RAAF order for British equipment, including the latest Mk V COL, was dependent on availability and delivery times were uncertain.

On news of the Japanese attack on Pearl Harbor, scientists at RPL began building an AW radar set by modifying the electronics of an experimental coast defence radar developed by the army. The rough but effective AW set was completed in a week and provided Sydney’s first air warning system. The Australian-designed AW Mk I radar was developed from this. The AW Mk I was based on the same aerial array as the army radar, but with a simpler tower. However, the army aerial was built to maximize signals received from surface targets and was not ideal for air warning where high angle coverage was needed against aircraft.