12 inch Mk X Gun Breech Mechanism : HMAS Australia (I)

Brass and steel breech mechanism from a 12 inch main armament gun. The mechanism consists of the breech, and an interrupted screw breech block on a hinged mounting. The hinge side of the carrier is impressed 'N / B. L. 12. A. X & X.*' Impressed on the following line is 'NO 313 III'. The number 364 has been marked out. The final line is impressed 'R. G. F. [broad arrow symbol] 1910'. These are the description, calibre, register number and mark, the manufacturer's initials and the year of service. Manufacturer's details are also impressed on the cocking lever and on a round plate on the carrier.

This is the breech mechanism from one of the 12 inch main armament guns carried by HMAS 'Australia' (I). This mechanism was located at the rear of the barrel and incorporated a chamber into which a 12 inch shell was loaded. Although never fired in action, these remain the heaviest weapons ever possessed by the Royal Australian Navy.

The 12 inch B.L. Mark X gun has a breech screw of the Welin type with two projecting studs on the rear face of the breech-screw diametrically opposite which form the axis for the sliding blocks of the breech-screw lever. The Welin breech block was invented by Axel Welin in 1889 or 1890. Vickers acquired the British patents shortly afterwards.

The breech block is a stepped, interrupted thread breech. The Welin pattern breech screw has a larger thread in proportion to its length, which is the result of arranging segments at varying diameters along the breech screw. As the breech is a single motion screw, it can be operated much faster than other, previous, interrupted-thread breeches.

HMAS 'Australia' was built in Scotland from 1910-13. On completion she sailed for Australia and, on 4 October 1913, led the cruisers and destroyers of Australia's first naval fleet into Sydney Harbour for the first time. With the outbreak of the First World War, HMAS 'Australia' became the flagship of the force that captured the German colonies in the southern Pacific. She led a force which captured Rabaul on 13 September 1914 before proceeding to Samoa.

With no German forces left in the South Pacific, HMAS 'Australia' was deployed to the United Kingdom. En route she sank the German auxiliary 'Eleanore Woermann'. On 8 February 1915 she became the flagship of the 2nd Battle Cruiser Squadron of the Royal Navy's Grand Fleet. Her service with the Grand Fleet consisted of a series of frequent patrols and exercises. She was twice rammed, firstly on 22 April 1916 by HMS 'New Zealand'. This led to her missing the Battle of Jutland, the major British naval engagement of the war. She was rammed again by HMS 'Repulse' in December 1917. HMAS 'Australia' carried out experimental aircraft operations in 1918 and led the port column of the Grand Fleet at the surrender of the German High Seas Fleet on 21 November 1918.

Returning home in 1919, she suffered a mutiny upon reaching Fremantle, Western Australia. Quite obsolete, she became a training vessel in Westernport until scuttled off Sydney Heads on 12 April 1924.