in the road and highway systems provided better and more rapid means of transportation during the 1920s and 1930s. As a result of the improved roadways, the Bureau was able to better maintain aids to navigation, benefiting the service economically. The extension of electric lines into remote sections of the country provided a reliable power source for operating aids to navigation. By the 1920s and 1930s, the majority of light stations had electric service, reducing the number of staff necessary to operate the station. As ancillary buildings at many stations, especially shore stations, were rendered useless, the makeup of the light station began to change. In 1935, Putnam was followed in the Commissioner's position by a career Lighthouse Service employee, H. D. King, a former district superintendent. On 1 July 1939, the Service merged with the United States Coast Guard, which has since taken over the maintenance and operation of all U.S. lighthouses and lightships. World War II On March 15, 1942 the U.S. Lighthouse Service/U.S. Coast Guard tender Acacia was sunk by the German submarine . Flags All of the Lighthouse Services lightships and lighthouse tenders flew the United States Lighthouse Service flag, a triangular flag with a red border featuring a blue lighthouse on a white background. Any Lighthouse Service ship upon which the Superintendent of Lighthouses was embarked also flew the Superintendent of Lighthouses flag, a rectangular flag with a blue border featuring the same blue lighthouse on a white background. Rank insignia Rank insignia of officers were as follows in 1918: See also Confederate States Lighthouse Bureau References Further reading Hyde, Charles K., and Ann and John Mahan. The Northern Lights: Lighthouses of the Upper Great Lakes. Detroit: Wayne State University Press, 1995. . Noble, Dennis, Lighthouses & Keepers: U. S. Lighthouse Service and Its Legacy (Annapolis: U. S. Naval Institute Press, 1997) Oleszewski, Wes, Great Lakes Lighthouses, American and Canadian: A Comprehensive Directory/Guide to Great Lakes Lighthouses, (Gwinn, Michigan: Avery Color Studios, Inc., 1998) . Penrod, John, Lighthouses of Michigan, (Berrien Center, Michigan: Penrod/Hiawatha, 1998) . Penrose, Laurie and Bill, A Traveler’s Guide to 116 Michigan Lighthouses (Petoskey, Michigan: Friede Publications, 1999). Putnam, George R., Lighthouses and Lightships of the United States, (Boston: Houghton Mifflin Co., 1933). United States Coast Guard, Aids to Navigation, (Washington, DC: U. S. Government Printing Office, 1945). Wagner, John L., Michigan Lighthouses: An Aerial Photographic Perspective, (East Lansing, Michigan: John