Site Records

Site Name: RAF Bawdsey R7 ROTOR Radar Bunker

Alderton Marshes
OS Grid Ref: TM326397

Sub Brit site visit: 13th April 2004

[Source: Nick Catford]

In 1950, RAF Bawdsey was chosen to participate in the ROTOR programme which should have been completed by January 1952.

The Chain Home radar station that had been operational since 1937 would not be required for this programme and a new GCI station was built to the north of the old site. Work on the new R3 two level underground control centre began late in 1950. Bawdsey was designated a GCI/E site utilising the following radars: one Type 7 Mk3, five Type 13's, 2 Type 14's and one Type 54.

All the radars were to be clustered round the R3 control centre apart from the Type 7 which was remotely sited 2km north east of the site on Alderton Marshes.

A Type 7 aerial array over an R7 bunker with an IFF on A type 14 plinth and a sub station to the rear. Note the Type 80 radar in the background with a Type 13 height finders either side. This example is at RAF Wartling.

The transmitter, receiver and motor for turning the aerial array were located underground in a bunker designated as an R7 and known as a 'well'. Because of the distance from the main site, this radar required its own IFF and an Mk 10 IFF was mounted on a Type 14 plinth, turntable and cabin. This was located a short distance to the east of the R7 bunker with a small brick built electricity sub station alongside.

Type 7 aerial array with the post war (ROTOR)
modifications on either side
The Type 7 was developed in the early years of WW2 as parallel development of the Chain Home Low (CHL) radar by the addition of a height-finding capability and a Plan Position Indicator (PPI) display.

Early stations were transportable with a fixed version of the final Type 7 equipment being developed in 1942. The fixed stations comprised an Operations Building (Happidrome), a radar well and an aerial mounted over the well; the well housed the transmitter and the receiver.

Continuous tracking of targets was essential to the interception procedure and the aerial system had to provide gap-free cover. To do this an array consisting of 32 centre-fed full wave dipoles was used, mounted in four stacks, each with eight dipoles.

For transmission, the top four dipoles and the bottom four dipoles in each stack could be combined either in phase or in antiphase under the operator's control. This achieved overlapping beam positions and provided adequate gap filling. For reception the dipoles in each stack could be combined in four different ways providing beams at difference angles of elevation for height finding. Switching between beams was done automatically or on a pulse-to-pulse basis using a capacity switch in the feeders.

Pre-Rotor Type 7 Transmitter (RAF Sopley)

The antenna beam width was 15 degrees although a narrower beam width and greater range performance was provided for the ROTOR improvement plan by the addition of more stacks of dipoles on each end of the aerial.

Few R7 bunkers survive but that at Bawdsey can still be found in a wooded area alongside a farm track running between Middle Barn Farm and Poplar Farm on Alderton Marshes. The farm track from the east was improved by metaling and due to the weight of vehicles using the track three new bridges and a new culvert were built over drains on the marshes. The bridges are still in place, as is much of the road although the last section of embanked road approaching the site has recently been leveled and will shortly be cultivated.

Photo:The roof of the R7 bunker. The aerial array was mounted above the fourth aperture back. The apertures on the far right and in the foreground were for personnel access.
Photo by Nick Catford

The Type 14 plinth and the adjacent sub station are located alongside the track as it runs along one side of the wooded area; both are still in good condition although stripped of any original fittings. This is now the only surviving ROTOR plinth at Bawdsey. The R7 bunker is 50 yards to the west in a clearing set back from the track. There is some evidence of the original compound fencing.

The bunker is approximately fifty feet long by fifteen feet wide. The top of it is flush with the ground with a 3' high brick wall around the west and south sides. This wall is unique to Bawdsey and may have been to stop earth erosion from the surrounding fields covering the top of the bunker. There are six rectangular apertures and one circular aperture in the roof, the largest of these was for the pedestal for the aerial array. The two smallest apertures were for personnel access using a ladder which has been removed. All the apertures have been covered by a wire mesh frame to stop animals falling into the well.

The bunker, which is divided into three rooms, appears to have been stripped of all original fittings and in places there are a few inches of water on the floor.


  • Bob Jenner
  • Dick Barrett's 'Radar Pages' web site
  • RCHME Survey Report - RAF Bawdsey (AMES24) October 1995 (fully revised 1999)

For further pictures of the R7 bunker at RAF Bawdsey click here

For RAF Bawdsey GCI Rotor Radar Station click here
For RAF Bawdsey Chain Home Radar Station click here
For RAF Bawdsey Rotor period VHF/UHF transmitter/receiver blocks click here

[Source: Nick Catford]

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Last updated 27th April 2004

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