Many landing craft and landing ships used on D-Day were not built at major shipyards, as you might expect. Existing yards, whether operated by naval authorities or civilian shipbuilding firms, were working flat out building warships or merchant shipping. The Allied navies had to resort to other locations for building D-Day landing craft.
Above: A newly-built LCM(3) “in a southern boatyard” in the USA. Many landing craft used on D-Day were built in the USA, but a high proportion were constructed in the UK. (Photo: Library of Congress)
The landing craft used on D-Day were built on both sides of the Atlantic, in either the UK or the USA. They were made at dozens of locations in each country.
In the UK, First World War-era shipyards were reopened for building LCTs, which could be assembled using only basic facilities. Sections of hull were prefabricated off-site and then assembled at the construction site, often by structural engineering firms that in peacetime built bridges rather than ships. Smaller landing craft, such as LCAs or LCMs, were built at a much wider range of locations. Traditional yacht builders were among those that built many of the smaller, wooden types of landing craft such as the LCI(S).
Many landing craft and ships built in the USA were used at Normandy. Some were built on the US east coast, but others were ordered from companies situated on major inland waterways such as the Mississippi, Missouri, Ohio and Tennessee rivers, as well as in the Great Lakes region. After construction, newly-built vessels had to make long river journeys before they first reached the sea. One of the most famous landing craft-builders was Higgins Industries, situated in New Orleans and run by Andrew Higgins.