Engineering an artificial harbor in Normandy © Javier Gil/Alamy

For the 75th anniversary of D-Day, the beginning of the end of WWII, we’re focusing on the remains of a Mulberry harbour—one of the most impressive military engineering feats of the war. Knowing that the ability to land huge numbers of men, vehicles, and supplies would be crucial to the Allies’ success in the invasion of Normandy, Winston Churchill challenged his forces to come up with artificial harbors that could be towed into place and operational within days of the initial landings.