Copyright IWM - IWM Non Commercial License. CH 15332. http://www.iwm.org.uk/collections/item/object/205196699

Technology

During the Battle of Britain 13 Group Fighter Command HQ was a key part of the Dowding air defence system. The system was the world’s first, fully co-ordinated air defence system. It used information from numerous high-tech sources including

  • Radar
  • GPO telephone and teleprinter services
  • Radio direction finding and fighter location systems as well as
  • VHF radio
  • EHF radio

to plot and build a surprisingly accurate, standardised picture of incoming raids, intended targets and to subsequently co-ordinate and deploy sector squadrons and their aircraft to where they were most needed.

Gathering, standardising, disseminating and coordinating all of this involved not just fighter pilots and ground crews but radar technicians, plotters, teleprinters, fighter controllers, Anti-Aircraft and Royal Observer Corps Liaison Officers, 30,000 Royal Observer Corps members, pilot trainers, air raid precautions members, members of the public the Royal Navy and many more.

People played a massive role in making 13 Group HQ operate effectively but it was only as good as the information and technology at its disposal.

What follows is just a brief summary of some of the key technologies used.  We would encourage you to find out more via web searches and by reading the Battle of Britain pages on the RAF Museum website.

To understand the role of technology in the bunker and defending the skies a basic knowledge is needed of the structure of Fighter Command and the channels of information.

 

First level control

Fighter Command consisted of 4 groups, 10, 11, 12 and 13. Each Group had its own area of Britain to defend and was split into Sectors with RAF stations in each sector area, one of which was the Sector Control Station. Sector Control rooms could scramble pilots from not only the sector airfield but other airfields within their sector area. All the Sector Control Stations reported to the Group Headquarters, and they in turn reported to Fighter Command Headquarters at Stanmore in Middlesex, near London. The Fighter Command Headquarters also acted as a filter and communications centre passing information from radar intelligence down to Group level who could pass it down to Sector level.

Fighter Command HQ therefore had an overall battle / defence picture for all of the UK, Group had this for their area whilst sector had the front-line picture and tactical control. 

For a fuller account of the fighter control system please visit the website

  • Diagram showing the fighter command structure and flow of intelligence. Copyright: RAF (http://www.raf.mod.uk/history/fightercontrolsystem.cfm)
  • Map

Radar (RDF)

British physicist Robert Watson-Watt is often referred to as the "Father" of radar. Initially appointed by the Air Ministry in 1934 to develop a weapon in response to rumours of a German death ray machine, Watson-Watt instead began experimenting on the potential use of radar.

Radar relies on a transmitted radio signal being reflected back from an aeroplane, like an echo. This echo is then received and analysed to determine the aircraft's range, height and bearing. Whilst primitive at its time, the network of radar stations from the south west of England all the way to the north east of Scotland, Chain Home, cast a defensive net around Britain. Dowding had recognised the importance of early warning and radar and though at this time hard to interpret accurately, it gave crucial early intelligence on incoming raids.

Radar intelligence was reported direct to Fighter Command HQ at Stanmore who passed it to Group HQs. Groups HQs in turn passed it on to Sector control rooms.

As the raids got closer The Royal Observer Corps, often positioned on the coast, would then be the first to spot incoming raids and report further on range, height and bearing via telephone or VHF radio whilst those inland were able to help track the raids once they had passed over the coastline.
The combination of radar and spotters was very effective though Reichsmarschall Hermann Wilhelm Göering failed to recognis the importance of British radar or thought it too primitive in comparison to their own radar systems to be of any significance.

The observer corps reported to Observer Corps Centres who passed the information to Sector Control Rooms. Sector passed the information to Group level. Group then passed it up to Fighter Command HQ and the plots were successfully updated at Sector, Group and Fighter Command HQ levels. By the time raids were within Observer Corps line of sight it was important for Sector Operations to get the information first as they needed to react quickly and order their sector airfield or other airfield squadrons to specific states, raids, altitudes etc. (for example, radar could detect bomber formations over airfields south of the English channel, in France. Those bomber formations could make the English coastline within 10-15 mins but in order to reach optimal operational height fighter defence squadrons needed around 15-20 mins. Optimal height meant higher than the enemy which gave them an element of surprise and tactical advantage.) This clearly demonstrates that time is of the essence if controllers were to give the pilots and squadrons the best chance of advantage against an enemy that often outnumbered them.

So the communications methods and technologies employed to inform needed to be seamless.

The information from radar and Observer Corps was passed up and down the chain of command to allow the overall picture to be plotted and to ensure if one sector was knocked out of action, Fighter Command could still function effectively.

You can find more useful information about radar and its role in the Battle of Britain:

Radar the Battle Winner

How Radar Works

GPO Telephone and Teleprinter

With the vast amount of information going in and out of 13 Group HQ it was important to have a strong telecommunications infrastructure.

In 1937 Kenton Bar, Newcastle was identified as a possible location for the 13 Group Headquarters as the large number of telephone and signaling circuits that would be required for a fighter command HQ could easily be provisioned.  

Telephones were used to relay relatively non-sensitive information or scrambled to make the information more secure.
Teleprinters, an electromechanical typewriter that can be used to send and receive typed messages from point to point and point to multipoint over various types of communications channels were also heavily used. The WAAFs that operated these were the original ‘Computer Girls’ and teleprinters are seen as the forerunners to the computers of today. 

The messages all came in 5 letter code that needed to be interpreted. Each command group had numerous sector airfields and the teleprinter could be used to send secure messages to them as well as Group Fighter Command and even Bletchley Park, Churchill's Secret Intelligence and Computers Headquarters as well as other military establishments throughout the UK.  

Tote / State of Squadrons Board and direction-finding stations / fighter location system

Whilst plotters and controllers at Group 13 HQ received continual updates on the locations of raids from sector control rooms and from Fighter Command it was also important for the commanders and controllers at group and sector levels to know where the squadrons were, in a timely fashion. This allowed them to assess which squadrons were best placed to patrol or intercept at any given time and to pass around necessary orders and feed information back into the intelligence network.

Inside the 13 Group bunker the tote and state of squadrons board told them a number of pieces of vital information. The state of squadrons showed a tally of operational aircraft and pilots. This gave a solid indication as to the fighting strength of a squadron and its ability to regroup and rearm after a sortie.

The tote board showed at what state a squadron was at any given time. As a squadron achieved, or was ordered to a particular state, a set of coloured bulbs – red, yellow, blue or green were illuminated. 

  • Released – Released from operations
  • Available 30 mins – required in 30 mins or less
  • Available – Achieved the above state of readiness
  • Order to readiness – Required in 5 mins or less
  • At readiness – achieved the above state of readiness
  • Ordered to standby – Required in 2 mins or less
  • At standby – achieved above state of readiness
  • Ordered on patrol – Tasked with a pre-planned patrol
  • Left ground – successfully airborne
  • In position – in correct patrol area
  • Blank white – left ground over 15 mins (only when on pre-planned patrol)
  • Blank blue – left ground over 30 mins (only when on pre-planned patrol)
  • Blank yellow – Left ground over 45 mins (only when on pre-planned patrol)
  • Blank red – Left ground over 60 mins (only when on pre-planned patrol)
  • Detailed to raid – Ordered to attack a specific enemy formation
  • Enemy sighted – Airborne call confirming enemy sighted, followed by “tally ho” (attacking now)
  • Ordered to land – ordered to land
  • Landed and refuelling – Landed and refuelling

Four lights could be illuminated across every state on the tote board. These were for differentiating the different sections within each squadron. In general RAF fighter squadrons comprised 2 flights, A and B with 2 sections per flight, so 4 sections in total. 

In order to vector (direct) the defending fighters on to an incoming raid, the controller had to know exactly where they were. Direction-Finding or D/F radio stations allowed this. 

Pip-Squeak was the code-word for Identification Friend or Foe equipment installed in at least two key aircraft in each RAF Sector Station's Flight or Squadron. When enabled, Pip-Squeak regularly keyed the Hurricane or Spitfire radio transmitter for 14 seconds every minute. Three ground-based aerials in each sector allowed finding station operators, normally women from the Women’s Auxiliary Air Force, to take bearings from these signals, triangulate and determine the position of the Squadron Leader's aircraft and hence the general location of his Squadron. This information was then passed on by the WAAFs at the Direct Finding Station via dedicated GPO phone lines to the Sector Control Room where they were plotted on the general situation map. Updates were made up the chain to Group and Fighter Command in turn. The RAF refer to a transponder system, possibly the same thing, code-named Parrot with the instruction to switch it on being “Squawk your Parrot”. Either way, the transponder principle for identifying friend or foe is still in use today and is used in commercial airline / air traffic control. This is testiment to the soundness of the 1940s system. 

(Thanks to Duxford  Radio Society & RAF Museum for appropriate wording found at http://www.duxfordradiosociety.org/equiphist/pip-squeak/pip-squeak.html and http://www.raf.mod.uk/history/fightercontrolsystem.cfm ). 

  • Tote and state of squadrons board detail from Group 13 HQ bunker reconstruction images.

General Situation Map

The operations room contained a plotting table with a map of the group’s area and sectors.

With all the incoming and outgoing information plots were made on the board to represent flight path of raids, current position, altitude and raid number with similar being done to plot the friendly fighter squadrons. This gave a timely overview of what the general situation was and allowed discussions to happen and decisions to be made.

Blocks with yellow flags marked friendly fighters and noted their squadron number. 

On the blocks in our reconstructions, which were modeled from those shown at the Uxbridge, 11 Group HQ, bunker, there are two lines of text. The first line shows the raid number on enemy plots, the blocks without yellow flags, whilst the lower level text shows altitude. Some evidence from other bunkers shows enemy raid blocks which contain a third level of information stating the estimated enemy aircraft number.

These blocks and arrows were magnetic and the colours of the arrows related to the colours on the sector clock to show how up-to-date a plot was

  • Plotting table detail from Group 13 HQ bunker reconstruction images.