Incredibly rare 'Raid Block' and 'counters' used in RAF Filter and Sector Ops 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 it 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. Both wood and metal blocks were used during the war (as illustrated in a Secret Air Defence Pamphlet). This wooden block is of relatively basic construction, wedge-shaped and approximately 8cm long x 5cm wide x 3cm tall at the back, 0.7cm at the front. Stained black with a felt-like cloth on the base, it has integral grooves and a small depression into which plastic letter and number tiles can be placed, these tiles providing information such as the height and strength of a raid etc. In this case the black on yellow indicating hostile (enemy) aircraft. Other information could be added to the block in the form of plotting pieces on metal 'stalks' that were slotted into the holes at the end of the block. In addition to the block itself, we are offering the two tiles shown. The yellow one is handwritten with the number '926' to one side and is blank to the reverse. The smaller red tile is marked in white with the number '2'. The block is a little dusty but in excellent overall condition. A fantastic opportunity to create a small Operations Room display. If you are lucky enough to own a sector clock then this is a must have item. Stock code M25333-6.