Details

The monument includes an anti-aircraft rocket battery known as a ZAA battery,
and the control building for a bombing decoy site. Both were constructed in
the early years of World War II as part of the defences of the city of Bristol
against German air raid attacks. The ZAA rocket battery and the control
building are located in close proximity to one another at the western end
of the Mendip Hills some 25km south west of the centre of Bristol.
The ZAA rocket battery and control building were both part of a
sophisticated system aimed at diverting hostile air attacks away from
Bristol whilst at the same time drawing enemy bombers to within range of
anti-aircraft fire. In the event of an imminent air raid on Bristol,
lighting decoys were put into operation on Black Down, Burrington, to the
north of the ZAA battery and in the vicinity of Ashridge Farm to the south
of it. The lighting decoys, known as QL sites, attempted to simulate the
city lights of Bristol under black-out conditions and they included
devices to mimic the flickering lights of railway marshalling yards as
seen from the air (the surviving decoy sites at Black Down are the subject
of a separate scheduling). If the decoy was considered to have been
successful in attracting aircraft then pre-prepared fires (known as
Starfish or QF sites) were electrically ignited to create the illusion of
targets having been set alight. The Starfish and QF sites were operated
from control buildings placed at least 400m from the decoy fire.
A QL decoy site at Ashridge Farm, was intended to replicate the position of
the West Depot of Bristol's railway system when viewed from the air in
relation to the Black Down decoy (known as Burrington C82) which provided
other identifiable lighting patterns such as that for Temple Meads Station and
Bristol's East Depot. The QL site at Ashridge Farm was backed up by a Starfish
site although neither the QL nor the Starfish site survive; almost all decoy
sites were systematically cleared at the end of the War. However, the control
building for the Ashridge Farm decoy still stands adjacent to the ZAA battery
to the north of the farm. It is of the standard design for a control building
or bunker although it is missing its entrance wing walls and earth banking
which have been stripped away in the early years of the 21st century.
Comprising two rooms it is constructed of 0.35m thick brickwork with an
outer blast-wall protecting the single entrance. The field control room,
which is the room to the south, would have contained a stove, switchgear,
and other communications equipment but of these internal features only the
seating for the stove remains. The other room would have housed the power
generators and three surviving concrete bases indicate their position;
some galvanised ducting, probably for exhausts, survives attached to air
vents in the walls. The control building operated as one of three which
controlled the decoys, the other two being on Black Down, but unlike the
others it is considered to have had a dual purpose in housing the
operating circuits for the ZAA battery in addition to the circuitry for
setting decoy lights and igniting decoy fires.
The Z anti-aircraft rocket battery comprises 13 surviving octagonal rocket
projector firing bases (from an original total of at least 19) together
with the base of an ammunition store. The rocket bases appear, in a study
made by Russett in 2002, to be arranged on a regular 42 foot (12.8m)
grid although two pairs of bases on the extreme north of the array which
no longer survive were much closer together than this. Of the thirteen
rocket bases which are known to survive, five were present but buried
below topsoil at the time of recording by Russett although their position
has been plotted. The other eight were visible on the surface to varying
degrees with two about 90% visible. Each of the rocket bases conforms to a
standard design, this being an octagonal base of concrete about 2.6m in
diameter with a 1.2m square concrete ramp on one side of the base and a
flared concrete apron at the other. At the centre of the base within a
ring about 1m in diameter are six equally spaced bolt fittings for holding
the rocket projectors which were probably 3 inch (c.7.5cm) projectors for
fire against formations of bombers. Around the perimeter of each base was
either a cast iron protractor ring calibrated in degrees, or an incised
ring made by pressing the concrete with the raised lettering of one of the
cast iron rings. This arrangement would have allowed for the aiming of the
rocket projectors. Within the rocket array is a concrete floor of what is
considered to have been an ammunition store or fuse magazine. It has
dimensions of 2m by 5.7m and its outer walls have been reduced to
foundation level.
Considerable information regarding the location, construction, and operation
of World War II decoy sites and anti-aircraft batteries in the area of the
Western Mendip Hills may be found in archives held by the Public Record
Office. These archives have been subject to a national study by English
Heritage.
All barns and farm buildings and all fencing, gates, modern breeze-block
walls and hardstandings are excluded from the scheduling, although the
ground beneath all of these features is included.

MAP EXTRACT
The site of the monument is shown on the attached map extract.

Source: Historic England

Reasons for Scheduling

Although of comparatively recent date, 20th century military sites are
increasingly seen as historic survivals representing a defining episode in the
history of warfare and of the century in general; as such they merit careful
record and, in some cases, preservation. One of the more significant
developments in the evolution of warfare during this period was the emergence
of strategic bombing in World War II, and this significance was reflected by
the resources invested in defence, both in terms of personnel and the sites on
which they served. During the war, the number of people in Anti-aircraft
Command reached a peak of 274,900 men, additional to the women soldiers of the
ATS who served on gunsites from summer 1941, and the Home Guard who manned
many sites later in the war. A national survey of England's anti-aircraft
provision, based on archive sources, has produced a detailed record of how
many sites there were, where they were and what they looked like. It is also
now known from a survey of aerial photographs how many of these survive.
Anti-aircraft gunsites divide into three main types: those for heavy guns
(HAA), light guns (LAA) and ZAA batteries for firing primitive unguided
rockets or unrotated projectiles (UPs). In addition to gunsites, decoy targets
were employed to deceive enemy bombers, while fighter command played a
complementary and significant role.
The ZAA rocket projectors were introduced in 1940 as simple weapons, which
relied on the shotgun effect, using density of rocket fire against both low
and higher flying targets. Their emplacements reflected variations in the size
of ammunition (the two and three inch rockets) and the number and arrangement
of barrels. The two inch rockets had a role comparable to the LAA guns against
low level attack and dive bombing, while three inch rockets flew higher, and
had a role similar to HAA fire against formations of bombers. Many ZAA sites
were established on or adjacent to HAA sites or bombing decoys. At their most
substantial, sites would have comprised a regular arrangement of projector
emplacements and accompanying ammunition shelters, a manning hut for the radar
crew, a fuse magazine (for ammunition assembly) and a command post. Their
widespread layout was designed to minimise the danger to personnel and
structures from the back blast of rockets.
Over 50 ZAA batteries were built during World War II, a very small number of
which have remains surviving. Any examples with surviving remains are
considered to be of national importance.

The ZAA rocket battery 265m north east of Ashridge Farm is a particularly
rare example with only one other of its type known to survive in Britain
even though 50 ZAA battery sites are known to have been constructed in
World War II.
The battery, which retains at least 13 of its original rocket projector
bases, provides a possibly unique association within England of an
anti-aircraft rocket battery lying nearby to the remains of contemporary
bombing decoy sites with one control building, although partly damaged,
still standing and included within the monument.
The monument acts as a reminder of the measures taken in World War II to
protect, as far as possible, the citizens of Bristol from the worst effects of
aerial bombardment by way of deceiving the enemy.

Source: Historic England

Sources

Books and journals
Dobinson, C, 'Twentieth Century Fortifications in England' in Bombing Decoys Of WWII, , Vol. Vol III, (1996)
Dobinson, C S, 'Twentieth Century Fortifications in England' in Anti-aircraft artillery, , Vol. Vol I, (1996)
Russett, V, 'Charterhouse Environs Research Team' in The Z battery site, Tynings Farm, Cheddar, (2002)
Schofield, A J, Webster, C J, Anderton, M J, 'Somerset Archaeology and Natural History' in Second World War Remains on Black Down: A Reinterpretation, (1999), 271-86
Schofield, A J, Webster, C J, Anderton, M J, 'Somerset Archaeology and Natural History' in Second World War Remains on Black Down: A Reinterpretation, (1999), 271-86
Other
Held at NMRC, RAF, 3G/TUD/5332, (1946)

Source: Historic England