In his two great works on the Battle of the Atlantic,* Samuel Eliot Morison identifies May 1943 as the turning point in the fight against the U-boats of the Third Reich. In that month, North Atlantic convoy ONS-5 — which steamed through the U.S. Coast Guard's Station 2 — would survive a running battle against a series of wolf packs that began on April 28. Also in that month, Allied forces would sink a total of 41 U-boats. It was the beginning of the end, and May 1943 would become known as “Black May” among U-boat commanders.

Morison describes a confluence of events that led to this turning point and to ultimate Allied victory in the Atlantic. Included in Morison’s descriptions of technologies that contributed to victory over the U-boats are the 10-cm radar and “Huff-Duff,” or high-frequency radio direction-finding (HF/DF). Yet Morison devotes little ink to the Loran navigational system — precisely one paragraph composed of two sentences that do not mention any use of Loran in escort of convoy or in antisubmarine patrols in the Atlantic during World War II.

The Loran system in the North Atlantic began operation (i.e., entered initial, limited service) in October 1942 and became fully operational in spring 1943. Two little-known contemporary documents that are cited in Chapter 2 of Ocean Station by Michael R. Adams describe the uses of Loran in the battle against the U-boats.

The first document, Loran, Volume I: Early Electronic History and the Bridging of the North Atlantic and North Pacific, was prepared in December 1944 by the Office of Engineering, U.S. Coast Guard Headquarters, Washington, D.C., and subsequently published under “Restricted” status in May 1946 as The Coast Guard at War: Loran IV, Volume I, by the Historical Section, Public Information Division, U.S. Coast Guard Headquarters. In a series of photographs and captions that appear in the text, it is declared that Loran enabled at-sea coordination, or rendezvous, of escort aircraft and convoys, thus providing North Atlantic convoys with aerial cover: “1944: Victory in the Atlantic: Perfect air coverage by means of Loran removes the terror of the sneak submarine attack from the convoys and breaks the back of Hitler’s ‘Sea Wall.’”

The second document is a book titled LORAN: Long Range Navigation, edited by J.A. Pierce et al. and published as Volume 4 in the Massachusetts Institute of Technology Radiation Laboratory Series by McGraw-Hill in 1948. In Chapter 2, “History of Loran,” written by J.H. Halford et al., the authors summarize: “The Loran system was found to be useful not only for normal navigation but for rendezvous between convoys and escorting aircraft and surface vessels and for the accurate location of enemy shipping and U-boats.” Similarly, Loran greatly enhanced the navigational efficiency of aerial antisubmarine patrols during bad weather/overcast and thereby extended the patrol ranges and station-keeping times of coastal-based patrol aircraft.

It is possible that Morison was restricted from providing details about the applications of Loran in the Battle of the Atlantic; nevertheless, the lacuna would become a paradigm of the literature.

*The Battle of the Atlantic: 1939–1943 (Little, Brown; Boston, 1947; rev. ed. 1954) and The Atlantic Battle Won: May 1943–May 1945 (Little, Brown; Boston, 1956), Volumes I and X, respectively, of Morison’s series History of United States Naval Operations in World War II.