Air Ministry Reference 4M/4. Fighter Command Reference T.M. Incredibly rare One-Tier Raid Block as used in RAF Filter and Sector Operations Rooms during the Battle of Britain and beyond to display important information relating to an enemy raid. When details of aircraft were received at Group Filter Room level, the information was interpreted on a map table using plotting 'counters' in the form of coloured arrows, discs and shields. Arrows indicated aircraft seen over land by Observers or over sea by radiolocation. Shields indicated aircraft heard over land or sea by Observers and discs indicated circling aircraft. The colour of the plotting pieces related directly to those on the sector clock such that information was updated every 5 minutes. The raid block itself was normally positioned at the head of the plotting path and provided additional information such as strength, height and whether the aircraft were 'hostile', 'friendly' or 'unknown'. Various patterns of block were used during the war including wooden and one and three tier metal types. This block is made of thin alloy and is approximately 1"/25mm tall x 2"/50mm wide x 0.5"/15mm deep. The upper and lower edges are turned such that the block will accomodate plastic letters and number plaques/tiles. Please note that you are buying the raid block alone, the numbers and map are not included and are shown for illustrative purposes only. The block is in very good used condition and is a fantastic opportunity to create a small Operations Room display. Stock code M25963.