Australia planned to manufacture their own guns and by 1928 the Government Ordnance Factory had been built at Maribyrnong in Victoria and equipped with machinery bought from Great Britain. The factory was capable of manufacturing guns up to a calibre of 4 inches and the plan was to initially manufacture the 18 pounder field gun. Before work began the world-wide depression began to fall over Australia. Faced with the prospect of the factory having to close down and the loss of the expertise gathered over the past years, the administrators turned to the production of car components.

As Australia began to emerge from the depression the Ordnance Factory received its first order for guns from the Army. This order was for 24 of the 3 inch anti-aircraft gun which had been developed during World War I (1914-1918) and which by the 1930s had become the standard gun adopted by the British for ground defence against attack by aircraft. In the 1930s it had been modified to embody a new principle of gun construction known as autofrettage. This method of construction represented an important advance in gun design. Mr M.M. O’Loughlin, Works Manager of the Ordnance Factory was sent to Woolwich in 1934 to study the process. By the end of 1936 the autofrettage process had been well established at Maribyrnong and the first 3 inch gun, consisting of ordnance, mounting and four wheel travelling platform, was completed. Early in 1937 the first 3 inch gun successfully passed all its tests and was accepted by the Army.

completed in July 1939. These guns were fitted with a ‘Rocking bar’ sight, so that laying by telescope and Deflection and Fuze correction could be applied on the gun.

This successful production of the 3 inch anti-aircraft gun was an event of considerable historic importance since it marked the successful establishment in Australia of the technique of making guns. That the 3 inch gun was more or less obsolete by the time it was first made in Australia was not so serious as it might first seem. By making this gun the Ordnance Factory had gained experience that, in 1939, enabled it to turn with some confidence to the manufacture of the 3.7 inch anti-aircraft gun which had come into production in Britain in 1937.

With the start of World War II Australian 3 inch AA guns were emplaced around the defended ports and saw active service in Darwin, Rabaul and Port Moresby. They continued to be used throughout the war but were replaced in the active areas by the 3.7 inch anti-aircraft guns as they became available. They were withdrawn from service in 1945.