Turning Time into Information

At the heart of this system was the ‘sector’, or ‘colour change’, clock. Developed from 1918 by Major General Ashmore, the system was designed to assist ground control operations by translating the time of an aircraft sighting into a corresponding colour-coded sector. This information could then be transferred to a large plotting map, allowing Fighter Controllers to follow the progress and heading off aircraft formations at a glance.

Lot 638 is a rare WWII RAF Operations Room Type I ‘Sector’ fusee wall timepiece by F.W. Elliott Limited, Croydon, dated 1939 and inscribed in pencil suggesting that was used at RAF Binbrook. Its 14-inch cream dial is divided into triangular panels spanning five-minute intervals, arranged in a repeating sequence of yellow, blue and red. The dial also incorporates vertically aligned 13–24 hour numerals alongside a conventional twelve-hour chapter ring, with the crowned RAF and laurel spray cypher at its centre.

The clock is inscribed to suggest a connection to its wartime history. The turned mahogany surround has a hand-written pencil inscription ‘C. FLETCHER, BINBROOK, 1944’ to the verso, while further official markings to the case include the Ministry of Defence arrow and stores numbers. RAF Binbrook, Lincolnshire, was established as a Bomber Command station in 1940 and subsequently became home to several distinguished bomber squadrons, including Nos. 9, 12, 101 and 617.

The Type I sector clock was introduced circa 1935 and was superseded by the Type II variant by 1943. Most known examples were produced by F.W. Elliott Limited, which had begun manufacturing clocks for the RAF in 1935. The present example is particularly interesting in retaining the RAF laurel wreath bordered crest introduced in 1938, replacing the earlier winged motif.

A Second RAF Sector Clock

A further rare example is offered as Lot 641, a WWII RAF Operations Room Type I ‘Sector’ fusee wall timepiece by F.W. Elliott Limited. Dated 1938, it comes with provenance suggesting that it was formerly at RAF Turnhouse, Scotland.

Like Lot 638, the clock features a 14-inch cream silk screen printed dial with the distinctive yellow, blue and red five-minute sectors, vertically aligned 13–24 hour numerals and the crowned RAF and laurel spray cypher. The dial surface retains evidence of its service history, while a small file of provenance paperwork accompanies the lot.

Its possible association with RAF Turnhouse potentially provides a particularly compelling historical context. Located on the site now occupied by Edinburgh Airport, RAF Turnhouse played an important role in the defence of Edinburgh during the Second World War and is credited with bringing down the first enemy aircraft of the war. On the evening of 28 October 1939, a Heinkel III reconnaissance aircraft was brought down by Spitfires attached to No. 602 Squadron. The tracking of the aircraft which led to its interception may well have involved the use of the present timepiece.

The clock is likely to be one of the earliest examples bearing the RAF laurel wreath bordered crest, which was introduced in 1938. Its survival with supporting provenance therefore offers a rare opportunity to explore the use of these highly specialised timepieces within an operational RAF environment.

From Five Minutes to Two and a Half

The sector clocks formed part of a wider system in which time, observation and map plotting were closely integrated. Sightings reported by the Royal Observer Corps were recorded using coded counters, which were grouped within metal block stands and positioned on a large plotting map. Further counters indicated aircraft type, height, number of aircraft, whether hostile or allied, and designated track, while colour-coded arrows and discs represented direction and circling aircraft.

As additional sightings and radar detections were received, operators moved the counters across the map using magnetic rakes. The resulting display enabled Fighter Controllers to establish the movement of aircraft formations and make decisions about when to scramble interceptors. The colour coding allowed a complex and rapidly changing picture to be organised into timed groupings, helping aircraft remain on the ground until their deployment was necessary and conserving valuable fuel.

By the later years of the war, the increasing speed and volume of raids meant that five-minute intervals were considered too long for effective tracking. The coloured divisions were therefore halved to 2.5-minute intervals, as seen on Lot 639, a very rare WWII Royal Observer Corps Operations Room electric slave ‘Sector’ wall timepiece by Smiths English Clock Systems GPO Synchronome, London, dated 1944.

At 56cm in diameter, Lot 639 retains the characteristic yellow, blue and red colour sequence, but with doubled-up triangular panels representing 2.5-minute periods. Its mechanism differs significantly from the fusee clocks: the brass-framed slave mechanism incorporates a solenoid which advances the dial every thirty seconds.

The timepiece would have been used in tandem with a Synchronome electric master timepiece, which sent a pulse every thirty seconds to advance the slave mechanism. This arrangement allowed multiple slave dials to be connected to a single accurately rated master timepiece. The absence of an RAF crest at the centre of the dial indicates that the present example was intended for use by the Royal Observer Corps.

The Equipment Behind the System

The final lot in the group, Lot 640, brings the workings of the system into particularly clear focus. This very rare group of WWII operations-room map plotting counters, mostly dating from circa 1940–45, comprises 41 separate items, including raid block counters denoting ‘hostile’, ‘strength’, ‘height’ and ‘designation’, together with colour-coded discs and arrows and a nickel-plated steel block carrier frame. The group is accompanied by a modern photographic print of No. 11 Fighter Group’s Operations Room at Uxbridge, after the 1943 original oil on canvas by Charles Cundall.

These seemingly modest objects were integral to the sector clock system. The first counter was matched to the colour of the sector indicated by the clock at the time of a sighting, while additional counters recorded the characteristics of the aircraft and its designated track. Arrows indicated heading and discs could denote aircraft circling, with the colour coding providing a visual link between the map and the passage of time.

Presented alongside the three sector timepieces, the group of counters demonstrates the practical application of the system in the operations room, where accurate timekeeping was transformed into an immediate visual record of activity in the skies.

A Window into Wartime Operations

Together, these items provide an unusually complete insight into the technology and organisation behind Britain’s wartime aircraft tracking system. From the early Type I RAF sector clocks believed to have been used at Binbrook and Turnhouse, to the later 2.5-minute Royal Observer Corps slave clock and the coded plotting counters used to record aircraft movements, the group demonstrates the close relationship between horology, observation and military strategy.

These objects were designed for a very specific purpose: to make rapidly changing information intelligible at a glance. Their distinctive dials, colour-coded sectors and specialised mechanisms reflect the demands of an environment in which the ability to establish where an aircraft was, what it represented, and when it had been sighted could determine when an interceptor squadron took to the air.

As rare survivors of this highly specialised system, the four lots offer a compelling record of the ingenuity, precision and organisation that underpinned Britain’s wartime aerial defence.

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Auction Details

Thursday 10 September, 10.30am BST
Donnington Priory, Newbury, Berkshire, RG14 2JE

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