1915 to today

The story of the sector clock

A clock that showed, by colour, how old every air raid report was. Its story runs from 1915 to the watch on your wrist.

Jump to a chapter

1915

31 May 1915

Bombs fall on London.

The airship LZ 38 kills seven people. London starts to build a defence: guns, searchlights and lookouts who report what they see.

Houses destroyed by a Zeppelin raid in King's Lynn, January 1915
19 Jan 1915King's Lynn
Soldiers holding part of a German bomb in Great Yarmouth, January 1915
Jan 1915Great Yarmouth
A recruiting poster of 1915: a Zeppelin caught in searchlights over St Paul's Cathedral
1915Recruiting poster
A bomb-damaged house in Croydon, October 1915
Oct 1915Croydon
Next: 1916 · Airships beaten Chapters

1916

3 September 1916

The airships can be beaten.

Over Cuffley, Leefe Robinson sets the airship SL 11 on fire. Thousands of Londoners watch it burn.

Soldiers among the wreckage of the airship SL 11 at Cuffley, September 1916
3 Sep 1916SL 11, Cuffley
Lieutenant William Leefe Robinson
Lt William Leefe Robinson VC
The skeleton of a German airship brought down in Essex in 1916
24 Sep 1916L 33, Little Wigborough
Next: 1917 · The colour clock Chapters

1917

13 June 1917

Bombers by day, and a coloured clock.

Fourteen Gothas bomb London in daylight. In answer, every report becomes a marker on a map, coloured to match a clock, so its age shows at a glance.

A London anti-aircraft gun in 1917, described at the time as the terror of the Zeppelins
1917A London anti-aircraft gun
German airmen of the bomber squadron Kagohl 3 with a Gotha
1917Gotha crews of Kagohl 3
Bomb damage in Hither Green, London, October 1917
19 Oct 1917Hither Green
Next: 1918 · The RAF Chapters

1918

1 April 1918

The Royal Air Force is born.

The RFC and the RNAS become one air force. By the last raid on London, in May, observers, guns and fighters report to one map.

The Odhams printing works in Long Acre, London, wrecked by a bomb in a German air raid in 1918
28 Jan 1918Odhams printing works
A Zeppelin-Staaken R.VI Giant bomber in flight
1918A Giant bomber
Ground crew loading bombs into a German bomber
Loading a German bomber
Next: 1936 · Fighter Command Chapters

1936

14 July 1936

One system for the whole sky.

Fighter Command joins radar, observers, telephones and operations rooms into one chain.

The underground operations room at Fighter Command headquarters, Bentley Priory
Fighter Command operations room, Bentley Priory
Chain Home masts at Poling, Sussex
Chain Home radar masts, Poling
An Observer Corps observer reports a sighting to his centre by chest telephone
Observer Corps post
Next: 1939 · The WAAF Chapters

1939

28 June 1939

The women who ran the table.

The WAAF is formed. Its women will plot every raid, take the reports and watch the radar.

WAAF plotters at work in the operations room of No
WAAF plotters, No. 11 Group, Uxbridge
Plotters move the markers with long rakes around the map table, operations room at Rudloe Manor, 1943
1943Rudloe Manor
WAAF operators at work in a Chain Home receiver room, supervised by Flight Officer P
WAAF radar operators
Radar operator Denise Miley plots aircraft on the screen of a receiver at Bawdsey, 1945
A WAAF radar operator at the screen
Next: The clock · How it worked Chapters

5 min

The sector clock

Time you could see.

Red, yellow and blue, five minutes each, on the wall of every operations room. It told the room how old each report was.

A sector clock in a wooden case: twelve red, yellow and blue triangles, five minutes each
The sector clockTwelve triangles, five minutes each

How to read it

  1. 01Twelve segmentsRound the dial run twelve triangles, red, yellow and blue, five minutes each. The pattern repeats four times an hour.
  2. 02The colour under the handWhen a report came in, its arrow on the table took the colour the minute hand was in.
  3. 03The 15-minute ruleFifteen minutes later the hand was back in that colour, and the old arrows of that colour came off the table.
  4. 04Read at a glanceThe colour the hand is in now means under five minutes old. The colour before it, five to ten. The one before that, ten to fifteen.

Right now, by your clock

  • Red 0–5 min
  • Yellow 5–10 min
  • Blue 10–15 min

Why it matteredFighters had to be sent to where a raid was, not where it had been. One look at the colours showed which plots could be trusted.

The operations room of the Battle of Britain Bunker at Uxbridge, as preserved today: the sector clock on the board above the map table
The clock above the tableBattle of Britain Bunker, Uxbridge
Raid markers on the restored map table at the Battle of Britain Bunker, Uxbridge
Raid markers, Battle of Britain Bunker
A sector clock with twenty-four coloured triangles
A 24-triangle dial
Next: 1940 · Battle of Britain Chapters

1940

10 July – 31 October 1940

The system holds.

For sixteen weeks the Luftwaffe tries to win the sky. Every raid is on the table within minutes.

The Sector G operations room at Duxford, September 1940, at the height of the Battle of Britain
Sept 1940Sector G operations room, Duxford
Pilots of No
Sept 1940No. 19 Squadron pilots, Fowlmere
Condensation trails left by British and German aircraft after a dogfight, 1940
1940Contrails over England
WAAF telephone operators in the Sector G operations room at Duxford take reports from Observer Corps posts, September 1940
Sept 1940WAAF telephonists, Duxford
Next: Today · Our watches Chapters

Today

Uxbridge, today

From the operations room to your wrist.

Our dial keeps the sector clock's twelve segments, one for every five minutes, read at a glance. Designed in Great Britain.

Discover the collection
The No
No. 11 Group operations room, Uxbridge, today
Chapters