Details

The monument includes a maintenance site specifically built for landing craft
engaged in the 1944 D-Day landings during World War II. The maintenance site
includes an arrangement of parallel concrete piers called a `gridiron' on the
shore, to the seaward side is a concrete and steel mooring point called a
`dolphin'. The monument is located on the west side of Mylor harbour, opening
onto the major navigable estuary of the Carrick Roads on the south coast of
west Cornwall. The monument is divided into two separate areas of protection,
one of which extends below Mean Low Water. 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, enabling inspection, scraping and repairs to be
carried out. Records show that the gridiron at Mylor was built by a local
firm, E Thomas and Son Ltd, the work supervised by Mr Bernard Breakell,
formerly a Devonport Dockyard civil engineer.
Overall the gridiron measures 40.23m wide north west-south east and contains
nine parallel straight piers centred 4.88m apart. The piers, approximately 40m
long north west-south east slope gently down the intertidal shore and are
built of shuttered concrete, with casts of the shuttering planks on their
surfaces; each is of rectangular section, 0.61m wide, rising 0.76m from a
concrete bedding plinth extending 0.3m beyond the pier sides. Recessed along
the upper edges of each pier are opposed metal angle-brackets, 3.05m apart,
bolted together through the thickness of the pier and with bolt-holes facing
upwards to secure timbers formerly laid along the piers' upper surfaces though
subsequently removed. Between the piers' bedding plinths the shore surface was
consolidated with compacted clay and slate fragments. Limited excavation and
probing has revealed that across much or all of the landward third of the
gridiron the bedding plinths have been replaced by a continuous concrete apron
underlying all nine piers. A low concrete-block wall along the seaward edge of
the apron and linking the eastern two piers is understood to be a post-war
addition to the structure.
An aerial photograph of the gridiron in 1946 shows additional linear
structures extending from the landward ends of several piers, converging on
two points along the sea wall behind. This is considered to relate to
winching and mooring mechanisms by which landing craft were positioned on the
gridiron. The exposed landward ends of the western piers showed no surviving
remains from these structures in 2000.
The dolphin is centred about 25m beyond the seaward edge of the gridiron. It
rises roughly 6m from the lower shore, founded on a concrete plinth 1.5m high
and about 4 sq m in plan. From each corner of the plinth rises a steel pile
formed as a box girder by welding two channelled girders back-to-back. Close
to their upper ends, the four piles support a concrete platform
about 3 sq m and 0.4m thick; the tops of the piles project about 0.3m from the
platform's upper surface. Some piles retain remains of a thin concrete pad
bolted around the pile about 0.75m below the platform; these pads may have
supported fenders protecting the piles from impact when landing craft were
being manoeuvred beside them. A second dolphin, 67m to the south east, was
removed in 2001 following photographic recording.
The gridiron in this monument was partly buried across both ends following
construction of a hammer-head quay, the Admiralty Quay, in 1951, though much
of the gridiron remained exposed within the quay's eastern basin. During
redevelopment of the quay to provide a car and boat parking facility and
slipway in 2000, the eastern basin of the quay was infilled behind a new
retaining wall built over the east end of the gridiron; following detailed
recording, measures were taken to ensure the intact preservation of the
gridiron beneath the retaining wall and the infill deposits. This monument is
part of an interrelated group of sites along the Carrick Roads which provided
necessary facilities used by United States forces during the preparation and
execution of the D-Day landings. These facilities included another gridiron,
at Falmouth, and five embarkation points, called `hards', at various points
along the estuary.
All modern metalled surfaces, the oil interceptor, its drains and pipework and
all modern materials stored on the dolphins are excluded from the scheduling,
although the ground beneath them is included. All modern structures and
ground-raising deposits in the area encompassing the gridiron and which lie
above a plane 1m above the upper surfaces of the gridiron piers are excluded
from the scheduling, although the ground and all features beneath that level
is included.

MAP EXTRACT
The site of the monument is shown on the attached map extract.
It includes a 2 metre boundary around the archaeological features,
considered to be essential for the monument's support and preservation.

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 at Mylor harbour survives well as the
only such site nationally which retains one of its dolphins intact along with
the gridiron. The preservation of the gridiron by burial during redevelopment
of the modern quay above it provided a research opportunity resulting in this
monument being an unusually well-documented example of its class both
archaeologically and historically. It forms an integral part of a group of
maintenance and embarkation sites along the coast bordering the Carrick Roads,
together with camps and transit areas behind the coast, which reflected the
infrastructure necessary for successful preparation and execution of the D-Day
landings. The good survival of a range of these sites along the Carrick Roads,
in which this monument is an important component, provides valuable evidence
for the operation's strategic planning, the detailed physical nature of its
execution, and the dispersal and concealment of its key activities essential
to maintain secrecy from the enemy.

Source: Historic England

Sources

Books and journals
Breakell B, , Falmouth at War, (1990)
Other
Accompanies notes to MPP evaln visits, RAF, 1946 vertical AP of Mylor harbour with the gridiron & dolphins, (1946)
Annex 1 to notes for MPP evaln visits, Johnson N, D-Day Embarkation and Maintenance Sites, (1999)
Title: 1:10000 Ordnance Survey Map SW 83 NW
Source Date: 1973
Author:
Publisher:
Surveyor:

Title: Revised plan and notes of gridiron after exp of landward end at NW
Source Date: 2000
Author:
Publisher:
Surveyor:
Amends draft report in Source 2
Watts, M A & Exeter Archaeology, Arch Recording of WW2 Gridiron at Mylor Yacht Harbour, 2000, Unpub Exeter Arch draft rpt Oct 2000

Source: Historic England