Monument MPM1952 - Horsea Island D-Day Landing Craft Maintenance Site

The remains of Second World War landing craft slipways constructed on Horsea Island for the maintenance and repair of landing craft during Operation Overlord (D-Day).

Remains of Second World War landing craft slipways constructed on the south side of Horsea Island to support the D-Day landings that took place on the 6th June 1944. This was one of a number of sites that were constructed for the building, repair and maintenance of landing craft and ships during Operation Overlord (D-Day). The site on Horsea Island is believed to be the largest of these sites.

The surviving remains consist of the main concrete rib structures of the slipways and concrete tethering blocks. Foundations of associated buildings and roads to the maintance yards survive above the shore.

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D-Day, on 6th June 1944, defined the start of the final phase of the Second World War. It was codenamed Neptune and landed over 850,000 men, 150,000 vehicles and 570,000 tons of supplies on to the French beachheads. Vast numbers of vessels were required and sites were selected for the building, repair and maintenance of landing craft. One such site and believed to be the largest, was constructed on the southern foreshore of Horsea Island. A total of five grid iron slipways and their supporting infrastructure, were built on the foreshore and support buildings on land to the north. The slipways are of the broadside type and primarily consist of nine concrete ribs with iron pads. Concrete blocks supported a system of mooring posts, mechanical winches and iron rings, which were used to pull a landing craft up the ribs and clear of the high water line. One winch set survives to the west side of the site. Other sets existed to the centre and east end of the site but no remains have been found. Once on the slipway, the landing craft could be worked on at all states of tide, before being relaunched at high tide. Out in the main channel, approximately 200m south of the foreshore, there are three mooring dolphins (originally four) which would have been used for securing the landing craft while they waited for a grid iron. After the Second World War, the maintenance site was decommissioned and the buildings were removed. Photographs held by the National Archives, Kew, show the Horsea Island site on 12 June 1944, six days after D-Day and the start of Operation Neptune with three returned landing craft (LCT 889, LCT 1165 and LCT 790) in position on the grid irons. LCT 889 was at Sword Beach, the lead LCT of six carrying 33rd Field Regiment Royal Artillery. This unit fired their 25 pounder guns from the deck of the landing craft as the assault approached the shore, before landing themselves 75 mins (H+75) after the first landings. LCT 889, commanded by Sub-Lieutenant Jewsbury was damaged by underwater obstacles causing the engine room to flood and she was towed back to the UK. LCT 790, commanded by Sub-Lieutenant Brown, carried vehicles of the assault waves, landing at H+45. Four other landing craft maintenance sites, located in the West Country are designated as Scheduled Ancient Monuments (National Heritage List for England reference 1020050, 1020053, 1020912 and 1021076). Collectively, the five sites are thought to represent the full extent of purpose-built, D-Day broadside slipways. Horsea Island was in the ownership of the Admiralty from the C19, during which it was used as a gunpowder drying facility, a torpedo-testing range and as the location for three successive telegraph stations. In the later C20, the wider area underwent large-scale land reclamation, losing its island form. Port Solent Marina was developed to the north-west and a recycling facility to the north-east.

Details
D-Day landing craft maintenance site on the former Horsea Island, of 1943. PRINCIPAL ELEMENTS: the monument lies on the foreshore giving access to Portsmouth Harbour. It is formed of five, grid-iron slipways and a number of concrete structures, which would have aided the manoeuvring and securing of the landing craft. All the elements are in the vicinity of National Grid Reference SU 64062 03863. The scheduled area has been mapped as one main polygon which includes the five grid irons and adjacent concrete structures. Outside of this envelope, four outlying features (one to the west, one to the east and two on the bank to the north) have been individually mapped. DESCRIPTION: the slipways are arranged along the foreshore, with their ribs running south, down the slope and beyond the low water line. For reference they are numbered one to five from the west. Each consists of nine, parallel concrete ribs separated by a gap of 4m, which are approximately 85m in length, 0.5m high and 0.5m wide. The top surface has regular, rectangular iron pads, to assist the settlement of a landing craft (only a few survive). Each slipway is separated from the next by a gap of around 12m. To the north of the ribs there are a number of concrete structures, which were part of the infrastructure for guiding the landing craft on and off the slipways. There are seven square blocks which are around 4m by 4m and 2m high. Each has the vestigial remains of an iron post providing a tethering point for the landing craft mooring lines. Slipways one and two, have two; slipways three, four and five have one. Slipways one and three also have a rectangular block of around 6m by 4m and 2m high, each of which has a horseshoe-shaped iron fitting. The slipway one block is related to a winching point behind the bank which has two, square blocks of around 2m by 2m by 2m. One has an iron spindle and the other has an iron ring. Slipway three also has two, 6m by 4m by 2m high blocks which have vestigial iron fittings and are orientated north to south. Around 100m west of slipway one, there is a 1m x 1m x 0.5m concrete block with an iron mooring post, set close into the bank to the north. Around 100m east of slipway five within a subsidiary channel, there is a 4m x 4m x 2m concrete block with an iron mooring post.

Sources
Websites
Historic England Research Report - Horsea Island Second World War Landing Craft Slipways, accessed 20/2/2022 from https://historicengland.org.uk/research/results/reports/177-2020
Other
1944 Aerial photographs held at the National Archives, Kew.

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Concrete slipways constructed in 1943 in the south eastern corner of Horsea Island. In 1944 the slipways were used to refit and repair 38 landing craft that had taken part in the D-Day landings.

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<1> Small, Fiona, 2020, Horsea Island Second World War Landing Craft Slipways Portsmouth, Hampshire (Bibliographic reference). SPM589.

<2> Historic England, The National Heritage List for England (Index). SPM35.

<3> Ripley, Basil, 1982, Horsea Island and The Royal Naval (Bibliographic reference). SPM410.