Details

The monument includes the remains of a World War II Heavy Anti-aircraft
gunsite, documented in wartime records as `TN9 (Thames North) Hadleigh', which
is sited on a ridge of high ground known as Sandpit Hill, located to the north
of Benfleet Creek and Hadleigh Marsh along the Thames estuary.

The monument is in eight areas of protection. The first includes the four 5.25
inch gun emplacements sited in a square formation and the remains of
associated nissen huts. The emplacements mostly survive below ground, having
been infilled with soil. The outer edge of the north easternmost emplacement's
ammunition gallery is visible above ground level. Their design is known from
aerial photographs, the earliest of which dates to 1946 and shows the circular
gun platforms with their internal rectangular structures. The emplacements
have three levels: the upper level has the ammunition gallery from where the
crew loaded the gun; the spent cartridge trench forms the next level (this
includes a tunnel to the outside down which the spent shell cases were
disposed); the pit at the lowest level houses the power mechanism. The
gunsite's ammunition supplies were stored in nine ammunition huts positioned
in a row to the immediate north west of the emplacements. The bases of two of
these huts survive and are included in the scheduling. The surviving concrete
floor of the huts carries the impression of the corrugated sheeting originally
used for the superstructure.

The second area to the west of the 5.25 inch emplacements is a combined
Operations Room/Generator Block. This structure is built of heavy concrete
with steel-framed, shuttered windows and measures some 22m long and a maximum
of 15m wide. It belongs to the post-war period when the 5.25 inch gunsite was
upgraded as a response to the Cold War threat and replaced an earlier wartime
building.

The third area, which encloses the 4.5 inch gun emplacements and associated
structures, lies some 500m to the south west of the larger guns. Aerial
photographs taken in 1946 show four octagonal emplacements in a semi-circle
facing east towards the direction of incoming enemy aircraft. Each has five
ammunition recesses built into the internal faces of the surrounding walls and
is flanked by an integral bomb-proof shelter for the gun crew. In the centre
of the semi-circle are a number of buildings and structures, including the
command post. Now partly infilled, the two most southerly emplacements have
concrete enclosures still visible. The foundations of the other two
emplacements and elements of the command post and on-site magazine will
survive as buried features. The fourth designated area lies to the west of the
4.5 inch emplacements and associated structures and encloses a second on-site
magazine. This is a flat roofed concrete structure, partly below ground level,
measuring some 15m by 8m.

Four more protected areas lie in between the two sets of emplacements and
enclose four ancillary buildings: the first is the Gun Store, two are simple,
one-roomed structures, and the fourth is a water tower. The Gun Store is
constructed of concrete, with a heavy steel door and four steel-framed,
heavily shuttered windows on the southern side.

The accommodation area for the gun crews (a series of lightweight barracks
formerly located in between the two sets of gun emplacements) are not included
in the scheduling.

War Office documents relating to the equipment and manning of gunsite TN9
Hadleigh indicate that the four 4.5 inch guns were operational from 1940,
whilst the four 5.25 inch guns came into operation during the course of 1944,
with the latter being maintained as a Cold War deterrent during the post-war
period.

All modern fence posts are excluded from the scheduling, although the ground
beneath them 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 batteries for firing primitive unguided rockets
(so called ZAA sites). In addition to gunsites, decoy targets were employed to
deceive enemy bombers, while fighter command played a complementary and
significant role. Following the end of World War II, 192 HAA sites were
selected for post-war use as the Nucleus Force, which was finally closed in
1955.
The HAA sites contained big guns with the function of engaging high flying
strategic bombers, hence their location around the south and east coasts, and
close to large cities and industrial and military targets. Of all the
gunsites, these were the most substantially built. There were three main
types: those for static guns (mostly 4.5 and 3.7 inch); those for 3.7 inch
mobile guns; and sites accommodating 5.25 inch weapons. These were all
distinct in fabric, though they could all occupy the same position at
different dates, or simultaneously by accretion. As well as the four or eight
gun emplacements, with their holdfast mountings for the guns, components will
generally include operational buildings such as a command post, radar
structures including the radar platform, on-site magazines for storing reserve
ammunition, gun stores and generating huts, usually one of the standard Nissen
hut designs. Domestic sites were also a feature of HAA gunsites, with huts,
ablutions blocks, offices, stores and amenities drawn from a common pool of
approved structures. Sites were often also provided with structures for their
close defence; pillboxes are the most common survivals, though earthwork
emplacements were also present. The layout of HAA gunsites was distinctive,
but changed over time, for example to accommodate the introduction of radar
from December 1940, women soldiers from summer 1941, and eight gun layouts
from late 1942.
Nearly 1,000 gunsites were built during World War II, and less than 200 of
these have some remains surviving. However, at only around 60 sites are these
remains thought sufficient to provide an understanding of their original form
and function. This includes 30 of the 192 examples which continued in use
until 1955. Surviving examples are therefore sufficiently rare to suggest that
all 60 well preserved examples are of national importance.

The Heavy Anti-aircraft gunsite on Sandpit Hill is an exceptional survival of
its type in the country. The importance of the site lies in its complexity and
range of surviving gun emplacements and ancillary buildings. It not only
retains gun emplacements of the 4.5 inch variety (and also their associated
structures), but also a complete battery of 5.25 inch emplacements (and
associated structures), the latter being the only survivals of this gun
calibre in the county. In addition it also has an exceptional collection of
ancillary buildings, including a Gun Store (one of only two in the county), a
well-preserved on-site magazine adjacent to the 4.5 inch emplacements and the
post-war combined Operations Room and Generator Block.

Considered together with all other variations of Heavy Anti-aircraft gunsite
design, TN9 Hadleigh is one of only nine sites to survive (in any form) from
an original wartime deployment of about 40 HAA positions across Essex - a
pattern designed to combat German bombers en route to the capital, the Thames
estuary and other military targets in the south east of England. It provides
an exceptional insight into the development of anti-aircraft measures in the
region and is a significant, visible reminder of the nature of home defence
during World War II.

Source: Historic England

Sources

Books and journals
Dobinson, C S, Twentieth Century Fortifications in England: Volume 1.3, (1996)
Dobinson, C S, Twentieth Century Fortifications in England: Volume 1.3, (1996), 469-472
Dobinson, C S, Twentieth Century Fortifications in England: Volume 1.3, (1996), 469-472
Nash, F, World War Two Heavy Anti-Aircraft Gun Sites in Essex, (1998)
Nash, F, World War Two Heavy Anti-Aircraft Gun Sites in Essex, (1998), 57-8
CBA, , 'CBA' in Twentieth Century Fortifications in England, (1996), 469-472
Other
HQ 6th AA Division Location List, (1940)
June, Hunting Surveys Ltd., Run 37-052, (1960)
June, Hunting Surveys Ltd., Run 37-052, (1960)
May, RAF, 106G-UK 1496-4388, (1946)
Tyler, S, MPP Film , (2000)
Tyler, S, MPP Film, (1998)
Tyler, S, MPP Film, (1998)

Source: Historic England