[3] He was invalided from Aspinwall (Colón), Panama, in January 1860, and later was ordered to the sloop of war USS Cumberland, flagship of the Squadron of Observation at Vera Cruz, Mexico.

[4] In March 1861, he returned to duty on board Cumberland and with that vessel took part in the destruction of the Norfolk Navy Yard during the Civil War.

[4] For some time afterward, he was actively employed, both on shore and at sea, in the search for the notorious raider CSS Alabama, until he applied for duty on board the flagship USS Hartford.

[5] Major Heywood served on shore at Pensacola and was on board Hartford in the Battle of Mobile Bay, where he received the brevet rank of lieutenant colonel for gallant and meritorious services.

From 1865 to 1867, he performed duty on board various ships, serving as Admiral Farragut's Fleet Marine Officer on the European Station and later in the same capacity in the North Atlantic Squadron.

In April 1885, he organized, within twenty-four hours from the time of the order, a battalion of 250 Marines for duty on the Isthmus of Panama to open the transit.

[10] Despite Heywood's efforts, the declaration of war with Spain in 1898 found the Marine Corps ill-prepared for combat in terms of training with modern small arms, battle drills, and small-unit exercises.

[8] Designated the First Battalion, and commanded by Lt. Col. Robert W. Huntington, the unit was scheduled to make an opposed landing in Cuba to secure a harbor at Guantánamo Bay.

The Panther proved to be a poor substitute for a purpose-designed transport ship, and troop morale plummeted in the tight and sweaty confines of the Panther's holds; later that same year, Commandant Heywood would request in his report to the Secretary of the Navy that the USS Resolute, a converted passenger steamship, should be retained in naval service as a permanent troopship.

[11] Fortunately, during two stopovers at U.S. ports en route to Cuba, Lt. Col. Huntington managed to institute a schedule of rifle marksmanship, small unit training, and battle drills before the Marines made their assault landing on enemy shores.