Personal correspondence, mainly to Gladys Fargo Squiers during their courtship and later throughout their marriage and family life. Includes early letters from her father disapproving of their marriage proposal. Later correspondence focuses on the health of their children, financial matters, and the running of her business, Blue Hill Nurseries. Correspondence was frequent due to Rousseau working in the Canal Zone a great distance from family while performing naval duties. 1908 letter from Theodore Roosevelt congratulating Harry on his marriage to Gladys.

Navy correspondence from the early 1900s includes reports made to officers regarding routine construction of yards and docks. When transferred to the Canal Zone there is substantial correspondence with George W. Goethals on congressional appropriations regarding funding for the Canal as well as personnel matters.

Navy correspondence from the late 1910s and 1920s includes a mix of personal and business matters from fellow officers within the U.S. Navy while Rousseau was stationed in Washington D.C. Correspondents include Rear Admiral Frank T. Chambers while District Public Works Officer at Pearl Harbor, Meriwether Lewis Walker, Governor of the Panama Canal Zone, and Lieutenant Commander Stephen S. Yeandle. Other correspondence refers to procurement, letters of recommendation, and attending various social functions including regattas and football games.

As Director of the Petroleum Reserves, the subject of the Teapot Dome scandal appears in letters from 1927 following high profile criminal trials in the press. Rousseau corresponded with members of the Pan American Petroleum Company in execution of his duties. Furthermore, one can see larger Naval policies around oil which would become a contributing factor in the coming conflict with Japan during World War II.