Thurrock Goes To War by Roger Reynolds and Jonathan Catton (published in 1997) gives a detailed account of the people and events that defined Thurrock’s role in the Second World War. D-Day forms a small but interesting section in this story. Perhaps the best known activities concerned the floating harbours code-named Mulbery and the PLUTO pipeline which supplied petrol to the allied armies in France. Tilbury was one of the centres of production for both of these. There is a little more on the Tilbury and Chadwell Memories web site.
Reynolds and Catton also mention the build up of traffic bound for the Normandy beaches during the weeks and months preceeding D-Day. This topic has been picked up in a blog post from the Essex Record Office. This includes their document of the month – a detailed map of the marshalling areas around the Port of Tilbury. Although described as a map of Tilbury, it actually covers most of Thurrock.