Details

The monument includes a maintenance site built beside the River Tamar estuary
at Saltash in south east Cornwall to service landing craft during the
preparations, engagement and aftermath of the 1944 D-Day landings during
World War II. The site includes an arrangement of parallel concrete piers
called a `gridiron', an adjacent mooring frame and a small quay, grouped on
the western shore of the River Tamar, partly beneath and extending north from
the modern suspension road bridge across the river. Operating from 1943 to
1945, the monument formed part of the Saltash sub-base of the United States
Naval Advanced Amphibious Base (USNAAB) at Plymouth.
The gridiron was designed to allow landing craft to be floated over it at high
tide then moored, coming to rest upon it as the tide fell and enabling
inspection, scraping and repairs to be carried out. Overall the gridiron
measures 54.3m wide, NNW-SSE, and contains 12 parallel straight piers
centred 4.85m apart. The piers, approximately 34m long north east-south west,
slope gently down the intertidal shore and are built of shuttered concrete,
with casts of shuttering planks where their surfaces are sufficiently well-
preserved. The seaward 18m of the southernmost pier was removed for
construction of the Tamar Bridge. Each pier is of rectangular section, 0.61m
wide, rising to 0.72m from the foreshore surface though also overlain in
places by shingle banks and riverine mud. Recessed along the upper edges of
each pier are opposed metal angle-brackets, centred 3.2m apart, bolted
together through the thickness of the pier and each with four bolt-holes
facing upwards to secure timbers formerly laid along the piers' upper
surfaces. At the seaward end of the sixth pier from the north, a horizontal
metal pin is supported above the pier surface by two short upright brackets.
An aerial photograph of 1946 confirms the gridiron's original complement of
12 piers. It also shows, close behind the landward side of the gridiron,
two small, bright features considered to have been mooring structures: one
beside the end of the northern pier and since removed; the other at the end of
the eighth pier to the south. This latter structure survives to 1.75m high as
a framework of square-section timber posts: two vertical uprights, spaced 0.3m
apart east-west, braced to north and south by two sloping timbers which meet
in the gap at the top of the uprights. The whole assemblage was pinned
together by four metal ties through the top and a timber block maintained the
spacing at the base of the uprights.
Immediately behind the gridiron's southern four piers is a small raised quay,
also visible on the 1946 aerial photograph. The quay is 20.5m long, NNW-SSE,
by up to 13.7m wide, faced on the east, towards the gridiron, by a vertical
shuttered-concrete revetment wall, 2.15m high; the quay's northern wall
comprises coursed end-set slabs. Smooth concrete facing at the quay's north
east corner reflects later refurbishment. The quay has a flat turf-covered
surface, with a sloping ramp at the south forming a slipway beside the
southern end of the gridiron. Cobbles set in concrete on the slipway surface
provided grip.
This maintenance site constituted a key part of the Saltash sub-base, one of
three maintenance and repair departments of the USNAAB at Plymouth, whose
various facilities were built by the 29th and 81st US Naval Construction
Battalions. Records indicate that the Saltash sub-base was set up in November
1943 under the command of Lt Com T H Harris, to service and repair landing
craft for infantry and tanks and to service minesweepers. The overall USNAAB
at Plymouth was commissioned as a major focal point in preparations for the D-
Day invasion, providing a range of shore-base and supply facilities before,
during and after the invasion. Throughout this period the base also provided
service and repair facilities, as in this scheduling at Saltash, for the
numerous craft and vessels involved in the invasion. The strategic value of
the USNAAB at Plymouth lessened as the Allied forces advanced across Europe
but the Saltash sub-base is recorded as remaining in operation to the end of
the war though on greatly reduced personnel, eventually closing on 31 August
1945.
The Tamar Bridge, the steps and their railings that ascend from the quay, and
all modern signs and mooring lines 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

D-Day, June 6th 1944, is one of the most significant dates in modern history,
defining the start of the final phase of World War II in Europe. After 2-3
years of preparations, the assault phase of `Operation Overlord' - codenamed
Neptune - lasted for little over three weeks and by 30 June had landed over
850,000 men on the invasion beachheads, together with nearly 150,000 vehicles
and 570,000 tons of supplies.
Sites used for the building, maintenance and repair of landing craft and
landing ships were essential to developing and retaining a fleet capable of
delivering Prime Minister Churchill's `great plan'. With so many vessels
involved (landing craft and landing ships principally, but there were 46
different types in all), construction and maintenance were significant tasks.
Contemporary descriptions refer to unprecedented levels of maritime activity,
with every port, harbour and boatyard being involved, in addition to beaches
and the streets of coastal towns and villages. The more substantial sites were
either in largely unmodified dry docks or on specially built `gridirons' or
slipways. The gridirons were used for maintenance, and took the form of a
series of parallel concrete slipways running down a slight gradient into the
water, allowing the boat to be floated on at high tide and repaired at low
tide; some were supplied with a winch mechanism for pulling vessels onto the
grid, and steel mooring points (`dolphins') for securing them when afloat.
Recorded examples include sites on the Rivers Dart (Devon), Tamar and Fal
(Cornwall), and in Portsmouth Harbour. Slipways, with a metal rail, winch
mechanisms and dolphins, used for landing ship repairs, are recorded on the
River Dart. However, much construction, repair and maintenance work was
conducted on an ad hoc arrangement and leaves little trace: for example,
landing craft (assault) - LCAs - were small vessels constructed and repaired
mainly in back streets and improvised hards at the water's edge.
Although in military archaeology fixed defences will often survive better than
materiel representing the mobile offensive, sufficient of the preparations for
D-Day in England remains to give an impression of the scale of the Operation,
and the variety of the specific tasks involved. All sites where surviving
remains provide an impression of the scale and nature of the preparations for
D-Day will be considered of national importance.

The D-Day landing craft maintenance site, 170m north of Saltash Pier survives
well, retaining its coherent grouping of related structures, clearly visible
and barely affected by later activity. The gridiron retains all 12 piers, most
to full length and with only limited truncation of the southernmost pier from
the later bridge-building. Its physical survival is complemented by valuable
recorded detail about the site's operational history and its wider context
within the US naval base at Plymouth, making this maintenance site a
well-documented example of its class. The historical records emphasise this
site's role as an integral part of the overall maintenance and embarkation
facilities along and behind the coastline bordering the Tamar Estuary and
Plymouth Sound, together forming the infrastructure necessary for successful
preparation and execution of the D-Day landings.

Source: Historic England

Sources

Books and journals
Clamp, A L, 'Plymouth during the Second World War series' in United States Naval Advanced Amphibious Base Plymouth 1943-45, (1994)
Dobinson, C S, 'Twentieth Century Fortifications in England' in Operation Overlord, , Vol. 5, (1996)
Other
In letter 10/8/1999 to A J Schofield, Nick Johnson CAU, Suggestion regarding classification of D-Day hards & gridirons, (1999)
RAF, 1946 RAF vertical AP of the Saltash railway bridge area, (1946)
Title: 1:10000 Ordnance Survey Map SX 45 NW
Source Date: 1983
Author:
Publisher:
Surveyor:

Title: 1:2500 Ordnance Survey landline mapping, centre point SX43325886
Source Date: 2000
Author:
Publisher:
Surveyor:

Source: Historic England