2-pounder "pom-pom" guns. A mixture of .303-inch machine guns were carried for close defence work: initially this consisted of four Vickers machine guns and twelve Lewis machine guns, although four Lewis guns were later removed. During a refit in 1942, two multiple pom-poms and five 20 mm Oerlikons were added to enhance the anti-aircraft armament. Four 3-pounder quick-firing Hotchkiss guns were used as saluting guns. Two sets of quadruple 21-inch torpedo tubes were fitted. Depth charges were carried: these were deployed by rails. The cruiser was designed to carry a single amphibious aircraft: initially a Supermarine Seagull III aircraft, but this was replaced in 1936 by the Supermarine Walrus. However, the aircraft catapult was not installed until April 1936, during a refit in Sydney. Before this, the Seagull amphibian was lowered into the water by the ship's recovery crane and took off from there. Armour aboard Canberra was limited to an armour deck over the machinery spaces and magazines, ranging from in thickness. Armour plate was also fitted to the turrets (up to thick) and the conning tower ( thick). Anti-torpedo bulges were also fitted. In 1924, the Australian government ordered two Kent-class cruisers to replace the ageing light cruisers and . These ships were to be named and Canberra, with both to be built by John Brown & Company, at their shipyard at Clydebank, Scotland: the only two County-class ships built in Scotland. Canberra was laid down on 9 September 1925, and given the yard number 513. Canberra was launched on 31 May 1927 by Princess Mary; the first ship of the RAN launched by a member of the Royal Family. Work on the ship was completed on 10 July 1928, the day after the cruiser was commissioned into the RAN. Most of the initial ship's company came from Sydney. Canberra cost approximately A£2 million to construct. Operational history Pre-World War II Canberra left Portsmouth on 4 December 1928, after several months of workup trials, and arrived at Sydney on 16 February 1929. The cruiser operated primarily in Australian waters during the next ten years, spending periods of time as the RAN flagship. On 20 September 1929, during a round-Australia cruise, the ship grounded on a sand shoal outside Roebuck Bay, Western Australia. The damage did not prevent the ship from operating, and it was not until early 1930 that the affected hull plates were replaced. In September 1931,