Did a search od Sousa, Souza and nothing then did as instructions said one could do and used only first 3 letters: Sou Result: Sousie, D. Rank: Landsman Place: not entered County: unknown Unit: Michigan Naval Reserves
From Wikipedia on Navy Reserve: "With the lack of any major threat to the United States in the post-Civil War years, the U.S. Navy took on the appearance and missions of the force it had been in 1860. Then came publication of naval theorist Captain Alfred Thayer Mahan’s landmark study The Influence of Sea Power Upon History, which in part prompted a modernization of the U.S. fleet and brought some of the first calls for an organized naval reserve to help man these more advanced ships. In the meantime, state naval militias represented the Navy’s manpower reserve, demonstrating their capabilities during the Spanish-American War in which they assisted in coastal defense and served aboard ship. Militiamen from Massachusetts, New York, Michigan, and Maryland manned four auxiliary cruisers—Prairie, Yankee, Yosemite, and Dixie—seeing action off Cuba. All told, some 263 officers and 3,832 enlisted men of various state naval militias answered the call to arms."
His SpA Rank of Landsman is the same as Seaman Apprentice today.
The Michigan State Archives should have more. If he was assigned to a ship that saw action his unit would have been "Federalized" and his service record may be at the NARA now. Navy/Marine Service records were not stored there in 1973 when they had a fire so should be available.
Most likely if he was aboard a ship it would have been the USS Yankee. Website below has SpA War Navy Ships: http://www.spanamwar.com/usnavy.htmhttp://www.spanamwar.com/usnavy.htm