Lt. George Dewey, who would later command the American attack on Manila Bay during the Spanish-American War, "conned" (navigated, I assume) the USS Mississippi during the Civil War. At New Orleans, the Mississippi destroyed the Confederate ironclad ram Manassas.
What if Dewey was killed at New Orleans or at some other point in the Civil War? Assuming the butterflies are minimal, someone else will command the U.S. fleet at Manila Bay, which might be significant later when all sorts of shenanigans involving foreign ships broke out later.
(Among other things, the German ships were maneuvering aggressively and nearly provoked a fight.)