Due to inadequate American defenses, U-boat sailors enjoyed the longest sustained period of success in their commerce war against the Allies during the Drumbeat offensive off the eastern seaboard of the United States in the spring and summer of 1942. Often using their deck guns to conserve torpedoes, U-boat skippers attacked Allied merchant vessels almost at will. Ultimately, the carnival-like atmosphere changed when the Americans began using their limited air and sea escort forces more efficiently. In the summer of 1942, a number of U-boats were caught on the surface with their crews lounging on deck. In one case, a U-boat was actually sunk by a slow-moving U.S. Navy blimp—one of the few blimp successes of the war.