Royal Observer Corps

The Royal Observer Corps was a Civil Defence organization (part of the Special Constabulary) which worked closely with Fighter Command. One of the first necessities in air defence was the constant information on the number, course and height of hostile aircraft. In order to obtain this information, a number of Observer Posts were set up in areas liable to attack. Each post was connected by direct telephone line to an Observer Centre. The Observer Centre would then pass on the information to Fighter Command.

During pre war exercises, things were quite relaxed. It was not essential to identify aircraft – Centre was not fussy as long as it was stated that it was a monoplane or biplane, single or multi engine. Things changed suddenly on 24th Aug 1939 when the code word “Readiness” was passed on by police to individual Observers and “the longest vigil in recorded history” began, which was to continue without break until May 1945.

Observers had to learn quickly on both using the Observer Instrument, aircraft height estimation and plane identification. At first observers improvised with cuttings from newspapers, flying magazines and any other publication from which information on planes could be gleaned. However it was not long before books/pamphlets/cards were produced showing plane silhouettes etc.

Observer Posts were formed into Groups. Each Observer Post was identified by a letter and numbered e.g. A1, A2, A3, B1, B2 etc. The strength of each Post should not have been less than eight nor more than sixteen observers, although it only required two observers on duty at a time to carry out the work of the Post. Two or three Posts worked together in co-operation to obtain accurate plots of aircraft. Posts in Suffolk came under the command of No 14 Group (ROC Control Centre – Old Guild Hall, Bury St Edmonds) and No 18 Group (ROC Control Centre – 8 West Stockwell Street, Colchester).

Above map shows the location of Posts in Suffolk (No 14 Group in red and No 18 Group in black).

No 14 Group: C2, Bungay; D2 Lowestoft; D3 Wrentham; D4 Pakefield; E1 Halesworth; E2 Southwold; E3 Westleton; F1 Badingham; F2 Saxmundham; F3 Wickham Market; G2 Stradbroke; G3 Debenham; H1 Bacton; H2 Crowfield; H3 Combs; J1 Stanton; J2 Beyton; J3 Bury St Edmunds; K1 Hartest; K2 Lavenham; K3 Clare; L1 Wickhambrook; L3 Haverhill; M2 Culford; M3 Kenford.

No 18 Group: F3 Sudbury; H1 Aldeburgh; H2 Orford; H3 Shottisham; J1 Claydon; L1 Grundisburgh; L2 Wolverstone; L3 Felixstowe

Each Observer Post was equipped with the following equipment:

Observer Instrument, grid squared chart attached to a circular table, telephone instrument and binoculars.

Left: ROC observers and the Observer Instrument. Middle: The Observer Instrument (photo kindly supplied by P Hibbs). Right: Aldeburgh Post
(H1) was in a purpose built tower.

The method of obtaining plots was as follows:

Low flying aircraft: the Observer instrument could not be used for low flying aircraft and in such cases the Observer Post had to estimate its position.

High flying aircraft: the position and height of high flying aircraft was determined by two or more Posts working together to obtain a ‘cross- plot’. In the diagram below, two Posts B1 and B2 are working together. The position of B1 is marked on B2’s chart and vice versa. B2 reports an estimated plot and height to Centre (by sighting the Instrument on the aircraft and then estimating the grid square). B1 overhears B2’s report to Centre and on his chart extends a line from B2-B2’s plot and then a line from B1 to the line of sight of B1’s instrument. Where the two lines cross is the actual position of the aircraft. With the actual position known, the ‘corrected ‘height can be read off the Instrument.

  Above: locating actual position of aircraft by 'cross-plots'

Aircraft reporting by sound: If aircraft can be heard and not seen, reports were still required. On each chart, a ‘sound’ circle with a 5 mile radius was marked. If the direction from which the sound appeared to come from could be ascertained, the pointer of the Instrument was set in this direction and the appropriate grid square noted. Centre would be able to work out the track of aircraft from reports received from various Posts.

The duties of the two observers on duty were as follows:

No 1 Observer – responsible for the working of the Post. He also watches and listens for aircraft and for visible aircraft will sight the instrument and set the ‘estimated’ height.

No 2 Observer – acts as telephonist and reports the position of aircraft as shown on the chart to Centre. He will also listen to reports from other Posts to obtain ‘corrected’ heights.

Observers wore a dark blue overall pattern uniform with a R.O.C badge and beret. Posts were to operate as long as the direct telephone line was intact or enemy action made continuing impossible. If forced to abandon their Post they could take part in the local defence – their uniform conferred rights and privileges of Armed Forces under International Law.

Home Forces could send messages via an Observer Post if no other means of communication was possible. The message would go via Centre to Fighter Command then GHQ Home Forces. Observer Posts sighting any airborne troops were to light a red fire work throwing out stars. A Home Guard Cyclist was to report to each Observer Post on ‘Action Stations’ – his duty to carry any information on enemy parachute landings to the nearest Home Guard Report Centre.

Air Defence of Great Britain – Instructions for Observer Posts, The Air Ministry, 1937
1939 – 1952. R.O.C Post Work, then and now, unpublished notes, Anon.
11 Corps papers, TNA
54 Div papers, TNA

observer posts
cross plots

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