The U-151 had been built to run the British blockade and minefields in order to carry cargo between Germany and the United States, but in April 1918 she set out on a mission armed with mines, torpedoes and two deck guns. From London, U.S. Admiral William Sims wrote to Washington on April 30 saying, “As there are only seven cruiser submarines built, we are able to keep very close track of these ships.