- Title: THE SCOPE AND PURPOSE OF THE FILTER ROOM [Main Title]
- Film Number: AMY 157
- Other titles:
- Summary: How radar is put to use during wartime. An explanation and detailed illustration of the roles and responsibilites of those involved with the operation of radar. Good scenes of activities in the plotting room (ie filter room) and plotting table.
- Description: The film opens with a Spitfire chasing a German twin engine bomber, with close up views of both pilots watching the other. The commentator notes that in high speed warfare it is vital to have good information and control of the pilot by the Royal Air Force (RAF) Fighter Control Section when seconds can matter to the outcome of serial combat. It is essential to protect the lines of defence beyond the coastline, and science has provided this in the form of Radar, illustrated in the film with views of Chain Home High (C H H) and Chain Home Low (C H L). Radar antennae towers and their associated operation stations. An incoming bomber has been detected and plotted as the alarm is raised at Portsmouth. Air raid wardens, fire brigade, Royal Observer Corps, anti-aircraft gunners respond accordingly, while civilians rush to the shelters, but the bomber has now been identified as one of ours and the crews are stood down. How has the radar been utilised, asks the commentry, the answer lies in the Filter Room. A Filter Room is shown with a large plotting table at the centre surrounded by many WAAF (Women’s Auxiliary Air Force) and RAF members at the table and on the overlooking balcony, simultaneously talking into their microphones, a cacophony of noise pervades all. The task of the Filter Room is to collate the radar data representing the detection of both enemy and friendly aircraft from all the C H H and C H L Radar stations. The data is represented on the plotting table by movable blocks, representing a single or group of aircraft, annotated with their relevant details, and are moved by WAAF operators as the data is updated. The Movements Liaison Officer (MLO) has a list of advance notification of friendly aircraft movements which he passes to the Senior Controller, overlooking the plot table, who indicates to the WAAFs below which of the plots (the wooden blocks) may be labelled as friendly. Other plots when proven enemy are likewise indicated. The tracks of the aircraft are thus established and are passed forward to the relevant Section Controllers at RAF Stations. All the data is recorded for intelligence and analysis purposes at a later time. The film moves to the Command/Operations room of an RAF fighter station. The plot table is seen, depicting South East England, Eastern English Channel and Northern France, and Sector boundaries, around which sit a few WAAF and RAF operators, with their Sector Controllers on the overlooking balcony. Responding to the data from the Filter Room, the familiar annotated wooden blocks are seen, each monitored by a WAAF / RAF operator who also have direct radio contact with the associated pilot when instructed by their Section Controller. The atmosphere is tense but mush more orderly than the Filter Room. The Filter Room also passes the filtered data to other Command, Group, Sector and Intruder Rooms, and the American Defence Wing Headquarters, film cuts to a large vertical map on wall with US Army personnel at work. The Royal Observer Corps and all those that need to know are advised notes the commentator. The film then proceeds to follow the events of an average day, with commentary on the developments. The Senior Controller is given a listing of the day’s friendly sorties by the MLO, sorts them out and directs a WAAF to plot them on the table. A Mayday signal is received, clip of Pilot in parachute as his aircraft crashes into the sea, pilot climbs into dingy, another aircraft circles above him. Returning to the Filter Room his location is plotted, and the rescue services alerted. Beachy Head C H L Radar, antennae towers seen in background, reports 30 plus at 20,000 feet to the Filter Room, the Senior Controller consults his listing and says that will be the Hastings patrol, film cuts to Spitfires flying in formation. A Spitfire on a weather reconnaissance flight Dieppe to Harwich is well behind his allocated schedule, and is detected by C H H radar stations and plotted as an enemy. The Control Room at RAF Tangmere scramble a flight of Spitfires, and alerts the Civilian authorities and the anti-aircraft gun battery. The pilot in the Spitfire over Dieppe is then seen singing happily to himself as he sets course for Harwich, and is very surprised when he is intercepted by the Spitfires from Tangmere who have been alerted by the Filter Room. With the weather reconnaissance Spitfire now recognised as friendly, the Tangmere flight return and an “All Clear” issued. In the Filter Room a WAAF plotter has asked if an incoming track has been correctly identified as friendly. The film cuts to a German twin engine bomber, the pilots discussing their target, Harwich, then returns to the Filter Room where the Senior Controller is worried about a cluster of symbols (the wooden blocks) on the plotting table near Harwich. The film returns to the German bomber as it drops bombs on Harwich, the Senior Controller says “bombs on Harwich” and the wooden blocks are updated to indicate Enemy. The weather reconnaissance Spitfire lands, reports an uneventful trip, totally unaware of the trouble he has caused by not reporting his deviation from schedule. The Senior Controller leaves to attend a meeting for a major offensive due to commence later that day, and summons the MLO to take control in during his absence. Personnel assemble in the briefing room. The commentary notes that the viewer has seen something of the work of the Filter Room, the accurate reporting and plotting of enemy aircraft can be difficult enough even when only a few aircraft are operating. How much more difficult this is when hundreds of aircraft are operating, keeping those who need to know, as it happens, is no easy task. The camera returns and pans round to show the complex nature of the Filter Room; wall charts for radar, aircraft movements, weather; the MLO section and the constantly changing situation on the plotting table, and as before, a cacophony of noise pervades all. Film shows C H H Radar Beachy Head reporting 80 plus bandits, C H H Radar Fairlight reporting 100 plus bandits, which are plotted on the table. The MLO reports American B-17 bombers en route to Germany, likewise plotted on the table. Cut to wall clock showing 1600 hours. A new contact south of Selsey Bill is plotted, film cuts to incoming Heinkel bombers flying low. The plot table is now crowded. More contacts reported and plotted, Filter Room estimates 30 plus Bandits, as Spitfires are scrambled from several RAF Stations. The plot table is very crowded, reflected in the aerial view of battle: Spitfires, German fighters, German bombers, American fighters and B-17 bombers wheeling about the sky, it looks chaotic, as does the plot table. Clock shows 1630 hours. 120 plus targets are estimated in the battle. An incoming target is located but not identified and causes concern until the pilot of the aircraft remembers to switch on the IFF transmitter (IFF), thus identifying a B-17 returning with engine trouble. Clock shows 1715 hours. CH Radar Willy reports 100 plus bandits, and three Y Stations have received an SOS from a B-17 about to ditch and are able to determine its position by triangulation. These events are duly plotted and the MLO is seen advising RAF Newhaven to initiate rescue procedures: A Lysander takes off and three RAF launches set out to sea. C H L Radar Dover reports low flying bandit from Calais and the MLO calls RAF Biggin Hill to scramble - and warns RAF Hastings, Ashford and Dover. The Filter Room gives the track co-ordinates to the MLO, who broadcasts them to the Fighter Station Aircraft Controllers. Film cuts to the German pilot who looks up to see two Spitfires above him as they shoot him down. The crew of a Whitley bomber believe they are south of Selsey Bill. This is confirmed by C H H Radar Poling North to the Filter Room Senior Controller, who thinks the aircraft is too far out at sea. The navigator is effectively lost, and with a failed port engine the crew realise they are in trouble. The IFF transmitter is activated and the Pilot asks for a “home in” signal to be relayed from their RAF Station. Film shows ground crew setting up a radar beacon that controls a searchlight: The radar antennae scans the sky until a return signal is received and the searchlight orientated in that direction. The Whitley crew locates the searchlight and safely land. The film closes as a new Senior Controller takes over and relives the other who has had a busy day.
- Access Conditions: IWM
- Featured Period:
- Production Date: 1944
- Production Country: GB
- Production Details: Royal Air Force (Production sponsor) Archibold Nettlefold Productions (Production company) Nettlefold, Archibold (Production individual)
- Personalities, Units and Organisations:
- Physical Characteristics: Colour format: B&W Sound format: Sound
- Technical Details: Format: 35mm Number of items/reels/tapes: 5 Footage: 1850ft
- Notes: Credits: shot at studios in St John's Wood, London NW8. Remarks: C H H and C H L Radar stations - Chain Home High was the codename for a series of fixed antennae radar stations around the coastline of Britain. A shortcoming was the inability to detect low flying aircraft, and was thus used in conjunction with the rotating antennae of the Chain Home Low radar stations. Y Station -Signals Intelligence collection sites. The interception of enemy radio traffic by multilingual operators, and passed on to the relevant Intelligence Agency, particularly to Bletchley Park, the Government Code and Cypher School. Summary: Eileen Younghusband was one of the WAAFs who was filmed at work in the filter room. Younghusband published two autobiographies about her wartime experiences 'Not An Ordinary Life' and 'One Woman's War', and has been interviewed on television about her experiences. She appeared on BBC Breakfast in 2011: https://www.youtube.com/watch?t=56&v=dRqC7sX0DaY
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