defence of South East Queensland during the Second World War, and to provide artillery training for Australian soldiers. Other fortifications throughout Moreton Bay during the war, included at Caloundra, on Moreton Island at Cowan Cowan Point and Rous. Together with the existing installations at Fort Lytton, they provided a coordinated series of defensive batteries for Moreton Bay.
In February 1939, six months before the start of WW2, a review of the defences of Moreton Bay called for two 6 inch Mark XI guns at north Bribie.
Soon after Australia declared war on Germany on 3 September 1939, 6 inch guns previously carried by the World War I-era cruiser HMAS Sydney were taken to the present location of Fort Bribie to guard the northwest channel, which ran close to the shore near Caloundra, across the bay in a southeasterly direction towards Moreton Island, and then southwesterly towards the mouth of the river, forming a Z-shaped route. The most effective sites for guns were the closest points to the channel bends.
The mounting and placement of the guns was hopelessly inadequate and according to Major General Robert E Jackson, Officer in Charge of Northern Command in July 1940, Fort Bribie was "no value from a defence point of view" and had to be fixed.
Before this could happen an argument about the location broke out, costings being sought for both Bribie and Caloundra. It was argued Caloundra was higher, better equipped and cheaper to build, whereas Bribie was flat, hot, infested with mosquitos and sandflies, had no freshwater, no bridge and would be much more expensive. The decision came down to Fort Bribie's ability to cover both entrances to the northwest channel, while Caloundra could only cover the most northerly entrance. The guns had a range of about 19 kilometres.
Colonel J S Whitelaw designed the layout of the fort on Bribie and recommended its completion, receiving the go ahead by early 1942. By April � hastened by
