3. Potomac became hazardous when the United States entered World War II
As soon as Germany declared war on the United States in December 1941, German U-boats appeared in frightening quantity along the North American coast. For the US Navy, the thought of the president cruising in his yacht unescorted was out of the question. Insufficient escort ships to protect needed convoys were available, none could be detailed to escort the president. FDR reluctantly agreed, and a search for a site for a new and secure presidential retreat began. There was at the time a camp which had been under construction by the Works Progress Administration (WPA), called Hi-Catoctin, near Thurmont, Maryland.
FDR personally visited the site in 1942, and decided that it was suitable. Several buildings had already been completed, and FDR took a personal interest in their conversion and the construction of others. Roosevelt had informed the press that the Doolittle Raiders who bombed Japan in early 1942 had taken off from Shangri La, a fictional utopia in the novel and film Lost Horizons. He returned to the theme when he christened the new presidential retreat with the same name. FDR used his winter vacation house in Warm Springs, Georgia, as the model for the new main lodge at Shangri La, and used the camp as often as he could.