This title may be a bit of hyperbole, but there is no doubt that the famous RAF Operations Room Plotting Clock made a significant contribution to the war effort... especially during the Battle of Britain. During World War II Great Britain was doted with carefully placed radar installations, aircraft observation posts, and special RAF Operations Rooms assigned to control the Royal Air Force's response to incursions by Nazi aircraft.

There were four Group Operations (Ops) Rooms during the Battle of Britain (two others came on line later in the war). These four Group Ops Rooms, and their many subsidiary Sector Ops Rooms, were charged with processing, organizing, and analyzing information received from the radar stations (via the Headquarters Filter and Operations Rooms in Bentley Priory) and other sources (calls from the Observer Corps, Direction Finding Station reports, Balloon Barrage reports, and so on). They were also charged with coordinating the aerial response to incursions by enemy aircraft via their subordinate Sector Operations Groups. An archival photo of the Uxbridge Group Operations Room is shown below left (Original in RAF Museum - Hendon). You can plainly see the special Group Operations Room Plotting Clock on the wall opposite the map table. The more recent image on the right, photographed by Nick Catford, shows the completely restored Ops Room at Uxbridge, with its Ops Room Clock in place.
The dial of these clocks, found in all RAF Ops Rooms of that era, had a very specific design intended to aid the complex efforts of RAF controllers. Information received by the Group Operations Room concerning the altitude, bearing and strength of approaching hostile aircraft were plotted on large table maps like that shown in the above photo. Group would then alert the most appropriate or its subordinate Sector Operations Rooms, who would take charge of the local response once their interceptor squadrons had been scrambled.

Work in the Group Ops Rooms must have been incredibly hectic. Numerous incoming messages had to be sorted, prioritized, and disseminated at a breathtaking pace. After all, late information could send a precious squadron of Hurricanes or Spitfires looking for hostile targets on bearings and at altitudes vacated by the enemy. A quick and reliable method of sorting stale information from current and more urgent reports was devised by the RAF, and the Ops Room clock was at the heart of this method.
Here's how it worked.

All incoming reports would be color coded with flags of either red, yellow, or blue according to the time they were received. These color-indicated times were assigned according to the position of the minute hand on the special Operations Room Clock which had its dial painted with triangles in this trio of colors at a succession of five minute intervals around the dial. The color indicated by the minute hand at the time the report was received would be the color given to the message and plotted on the Operations Room map. Because of the speed of these enemy raiders crossing Britain's coastline the RAF's response had to be made in minutes. This color coding process and the elaborate communications network behind it created a highly effective and efficient system. It was possible, according to reports from system veterans, to have fighters in the air and on their way to an intercept within five minutes of the initial contact. Without the simple yet elegant time coding system devised by the RAF, the British might not have been so successful in holding control of the skies over Britain during the crucial Battle of Britain as well as later in the war.
Comments and Suggestions to: Ned Frederick
Suggested Links:

RAF Uxbridge - Battle of Britain

Spitfire Cockpit Clocks

Battle of Britain web site (slow to load)

Guide to MoD Watch Standards