Developed by the British in World War II, “Mulberry harbours” were portable, temporary harbors that could be used for rapid on- and off-loading of cargo ships during the D-Day Invasion. The name “Mulberry” comes from the code name of the project in which the harbors were developed.

On D-Day, two premade harbors—dubbed Mulberry “A” and Mulberry “B”—were taken in sections across the English Channel and assembled off the coast of Normandy.

The development of the harbors was highly secretive.

The development of the harbors was highly secretive. At the time, some members from America’s Ghost Army were deployed two weeks prior to the D-Day invasion to simulate a fake harbor to draw German fire away from the originals.

Now, original pencil drawings of the Mulberry harbours are to be sold at auction. According to Britain’s Daily Mail, the sketches were drawn by Welsh engineer Hugh Iorys Hughes, and are being offered by an anonymous collector. The value of the drawings are estimaged to be between £40,000 and £60,000.

The drawings will be put on auction at Bonhams in New York on June 5.