LONDON, ENGLAND—More than 40 German U-boats and three English submarines dating to the First World War have been located along the southern and eastern coasts of the United Kingdom by Mark Dunkley of English Heritage and his team of researchers. Most of those vessels sank with their crews on board. At the beginning of the war, there were only 28 cramped, uncomfortable U-boats under the command of Kaiser Wilhelm II. By the end of the war, 380 U-boats were in use, and almost half of them were lost. Dunkley and his colleagues use sonar to measure the thickness of the hulls as they try to determine their condition. “We divers only approach the boats with great caution. Venturing inside would definitely be extremely dangerous,” he said.