Transmitter Buried Reserve at former RAF Stoke Holy Cross

Summary

Buried reserve transmitter block built in 1939 to an Air Ministry design from brick, capped with concrete.

Reasons for Designation

RAF Stoke Holy Cross Transmitter Buried Reserve is listed at Grade II for the following principal reasons:

Architectural interest:

* the Transmitter Buried Reserve structures reflects the importance of backup radar equipment ensuring an uninterrupted radar service during the Second World War.

Historic interest:

* the Chain Home Radio Direction Finding stations were decisive in providing early warning of Luftwaffe attacks, and the towers at RAF Stoke Holy Cross played a particularly crucial role in the air defence of the country during the Second World War, including tracking of V2 missiles late in the war.

Group value:

* with the listed remains of the transmitter and receiver sites which collectively make up RAF Stoke Holy Cross.

History

Chain Home was the name given to the network of Royal Air Force (RAF) early warning Radio Direction Finding (RDF) stations, later called radar, developed in the late 1930s. They were utilised throughout the Second World War, most famously in the Battle of Britain of 10 July 1940 – 31 October 1940. This was the world’s first use of radar technology in an operational early warning air defence system.

By the summer of 1936 Bawdsey Manor in Suffolk had been purchased by the Air Ministry and was in use as a centre for new aerial defence research, building on early successes achieved at nearby Orford Ness. It was at Bawdsey that the first working Chain Home station was completed, leading in August 1937 to the commissioning of a full chain of stations to be sited at roughly 40 mile intervals along the south and east coasts of England and Scotland. The station at Bawdsey became the prototype for the layout of equipment and buildings that was used throughout the chain. The transmitter and receiver blocks at Bawdsey survive, the transmitter is listed at Grade II* (NHLE 1245307), and the receiver at Grade II (NHLE 1245202).

Given the urgent need for the system to be operational as soon as possible, the Chain Home network was technologically quite crude, even by the standards of its day. Largely it used existing readily available components rather than those purpose designed for the task. Despite its rudimentary technology, the system was effective and could detect aircraft at an altitude of 15000 feet over 100 miles away. The requisites for a functioning station as developed at Bawdesy were a transmitter block broadcasting through aerials arranged over four 360 foot (109.72m) high steel transmitter towers, and a receiving block linked to four 240 feet (73.15m) high timber receiving towers. The stations transmitted using High Frequency (HF) long wave radio waves. There were four towers as it was originally planned for the stations to switch between four different frequencies to avoid enemy jamming of the signal. The transmitter towers were arranged in a straight line with the transmitter block centrally located off the line of towers. The receiver towers were in a quadrangular formation around the central receiver block. The transmitter aerials on the towers were accessed via three cantilevered pairs of platforms at heights of 15.2 m (50 feet), 60.95m (200 feet) and 106.67m (350 feet) up the towers. Initially, the aerials were held in cradles extended on an arm from the platforms, later they were suspended in arrays between towers in a ‘curtain’, fed by transmission lines leading from the transmitter building.

The requirements for a Chain Home Station site were that it should be on ground at least 50 feet (15.2m) above sea level, and close to the coast. The aerials transmitted radio waves in all directions, so reflections from below and behind (inland) would make the vital signals from the coast difficult to distinguish. The height of the aerials from the ground, and the ground being level or smoothly sloping allowed the downward reflection to be mitigated. A reflector curtain was positioned inland to the west, redirecting the radio waves back out to sea and avoiding confusing readings received from objects and higher ground inland. The result was that radio waves were pulsed out in a lobe with a fixed arc of around 100 degrees, centred on a ‘line of shoot’ bearing. The towers were immobile, so this line could not be adjusted. To ensure full coverage of the coast, each station’s range slightly overlapped that of its neighbours in the chain. RAF Stoke Holy Cross was complemented by stations at RAF West Beckham to the north and RAF High Street to the south.

RAF Stoke Holy Cross (Station 30) was added to the list of planned sites in December 1937 and the land acquired in the middle of 1938. Installation of equipment began in December 1938 and the site became operational (in an intermediate form, with two standing towers) in February 1939. Additional buildings and plant, including a buried reserve were planned from September 1939.

Initially the site was defended by eight Lewis guns, but these were supplemented by three Bofors 40 mm L/60 anti aircraft guns in July 1940 mounted on top of pillboxes constructed around the perimeter of the site. Dispersed accommodation sites were constructed in late 1939 to the south and east of the transmitter site.

The site was operational throughout the Second World War. A Bristol Blenheim aircraft hit transmitter tower number 2 on 18 July 1942 and crashed in adjacent fields. The crew were killed and the transmitter tower damaged. A replacement tower was constructed immediately to the east of the damaged tower. The equipment within the station was upgraded in September 1944 to help identify V2 rocket launch sites.

After the Second World War, RAF Stoke Holy Cross continued to function as a Chain Home station, albeit in a reduced capacity. It was handed over to RAF Fighter Command as part of Phase 1 of Operation ROTOR (the upgrading of the UK’s radar early warning system). The station closed in 1956, following the implementation of Phase 2 of Operation ROTOR.

The receiver towers were demolished in 1956 and 1957 and two of the steel transmitter towers were demolished in the 1968. A third tower was dismantled between 1989 and 1991. A microwave relay tower was built by the Post Office on the site of one of the transmitter towers in 1965, while reflectors on the surviving tower (Tower 4) connected radar stations at RAF Neatishead with RAF Staxton Wold and RAF West Drayton. The radar system was replaced in 1991 and the tower was repurposed. The entrance to the transmitter block was walled up and the surrounding protective walls were reduced in height in 2004. The transmitter block, transmitter tower bases and an adjacent air raid shelter were demolished in November 2022.

The Buried Reserve was constructed in 1940 to a standard Department of Works and Buildings design by Ernest Holloway in response to the threat of air raids on Chain Home sites. The purpose of the Buried Reserve was to house additional transmitter equipment for use should the main set become inoperative. The building fell out of use with the end of the Second World War.

Archaeological work carried out in advance of a housing development in 2013 identified the buried reserve as an extant but flooded buried structure. Historic building recording carried out in 2019, but the contractors could not access the interior of the structure. The internal flooding and relatively good condition of the exterior strongly suggests the interior survives intact.

Details

Buried reserve transmitter block built in 1939 to an Air Ministry design from brick, capped with concrete.

PLAN: The buried reserve comprises a stairwell opening into an operations room via a gas lock. Rooms containing an air conditioning plant and a latrine open from the operations room. An emergency exit leads to a ladder and hatch at the opposite end of the operations room.

EXTERIOR: The buried reserve comprises a concrete plinth with two concrete hatches on rollers, now sealed under a concrete cap. There is a ventilation tower adjacent, approximately 6.6m high and 0.67m square. Two smaller ventilator shafts, both now capped, sit to the east and west of the entrance hatches. The four bases of the reserve transmitter tower sit to the north east.

INTERIOR: The interior was not inspected as the entrance to the buried reserve has been sealed.

Sources

Books and journals
Dobinson, C, Twentieth Century Fortifications in England: Acoustics and Radar, (2000)
Dobinson, C, Building Radar: Forging Britain’s Early-Warning Chain, 1935-1945, (2010)
Gough, J., Watching the Skies: The History of Ground Radar in the Air Defence of the United Kingdom, (1993)
Anderton, M, World War Two Radar Stations - Survey Report, (2000)

Other
Hardy, R ‘RAF Stoke Holy Cross, Transmitter Buried Reserve, Poringland, Norfolk Historic Building Recording’ Unpublished Cotswold Archaeology Report 19019 February 2019

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