Museum and gallery staff put their favourite artefacts on display. Week 6: Admiralty Fire Control Table, HMS Belfast London.
The HMS Belfast guide book says that the Admiralty Fire Control Table (AFCT) is a mechanical computer, but it certainly doesn't look like one. What it resembles most is a table football game that has lost its footballers.
The AFCT was, in fact, a vital part of HMS Belfast's capability. The ship's strength lay in her powerful guns which have a range of over 14 miles and which helped to destroy the German battle cruiser Scharnhorst at the Battle of North Cape in December 1943. As well as leading the D-Day bombardment in June 1944, Belfast also bombarded North Korean and Chinese Communist supply lines during the Korean War. It was the AFCT which ensured that the guns would hit their targets and which helped the Belfast to gain her reputation with USAF spotter pilots as "that straight-shootin' ship".
So how did it work?
Information about a target's range, speed and bearing, relative to Belfast's own position, was received from the director control tower, or from the radar plot, and then fed into the AFCT by a crew of six. A complex series of hydraulically powered cams and gears was then activated, which translated the raw data into a continuous stream of instructions for the gun layers in the turrets.
Because it took several seconds for the shells to reach their target, the training and elevation instructions included an allowance, known as the "deflection correction", which anticipated the likely position of the target at the moment of impact. The AFCT also took into account outside air temperature and baromic pressure, wind speed and direction, and the number of rounds fired, all of which could significantly affect the accuracy of the guns at long range. It is hard to believe that this apparently primitive 1930s technology was still being used by the US Navy's last battleships at the time of the Gulf War.
A visit to HMS Belfast provides many surprises like this. It offers an opportunity to examine the fighting methods and everyday life of the Royal Navy during the 1940s and 50s. It is a period which seems long past, yet oddly contemporary.
Jo Hunt Jo Hunt is education officer of HMS Belfast, Morgans Lane, Tooley Street, London SE1 2JH Tel: 0171 940 6323