Though the tide was turning ever more quickly against U-boats, they were far from beaten. In fact, six of them were able to extend their range of operations to the coast of the United States. One of those was the U-155, the former German merchant submarine Deutschland which had loaded supplies in Baltimore in 1916. After the United States entered the war it was converted for service as a U-boat, and though slow in submerging and awkward to maneuver, it survived the war.
The U-151, under Lieutenant Commander Von Nostitz und Janckendorf, was the first of these submarines to patrol in American waters. It sailed from Germany on April 14, 1918, arriving on May 15 off the American coast, where it operated until July 1, when it set sail again for its home port.
In addition to its torpedoes the U-151 carried mines, and its primary mission was to mine the harbors of Baltimore, Philadelphia, and New York. With audacity that, looking back on it, gives a moment's pause, the German submarine made a submerged entry into Chesapeake Bay within gunfire range of Norfolk, Virginia, where the largest base of the United States Navy was located. The U-boat's entry was entirely undetected, although it sighted the cruiser St. Louis and two destroyers, and it made its way northward to the harbor of Baltimore, where it sowed its mines.
Returning to sea for the passage to Delaware Bay and Philadelphia, the U-151 encountered and destroyed two sailing ships, the Hattie Dunn and the Haupage, taking aboard seventeen sailing men, most of them Americans, as prisoners. Next the U-151 destroyed the steamer Edna, and the number of prisoners in the crowded submarine rose to twenty-three — more than half as many prisoners as submariners. Conversations in German, English, Danish, and Norwegian could be heard in different parts of the U-boat at the same time. Two of the prisoners, Americans originally from the town of St. George, Maine, had been boyhood friends but had not seen each other for thirty years before they were reunited inside the U-boat.
Once inside Delaware Bay the U-151 planted its deadly mines and headed for the harbor of New York. By June 2 the submarine had intercepted and sunk more ships and the number of prisoners increased. The time to put them off had come, and von Nostitz transferred them to the lifeboats of the Isabel B. Wiley and the Winneconne after these ships had been sunk.
By this time the presence of a U-boat off the American coast was well known, and the knowledge caused alarm among shippers. Navy ships and aircraft searched for the submarine but without success, and it continued to sink shipping. One of its victims was the Norwegian ship Vindeggen, whose cargo was 6,000 tons of copper, a scarce commodity in wartime Germany. Von Nostitz had the Vindeggen's seamen replace the submarine's iron ballast with precious copper bars, a process which took two days. Then the Vindeggen was sunk with explosives.
The U-151 returned to Kiel on July 20, 1918, after a voyage of thirteen weeks and three days. It had sunk by direct action some twenty-three ships, and its mines had accounted for four more.
The five U-boats that followed the U-151 also scored successes, including the sinking of the cruiser USS San Diego off Point o' Woods, Fire Island, New York, by a mine laid by the U-156. Their actions were a portent of what was to come some twenty-five years later in World War II.