On board the flagship, USS Hartford, during action against rebel forts and gunboats and with the ram Tennessee in Mobile Bay, 5 August 1864. Despite damage to his ship and the loss of several men on board as enemy fire raked her decks, Diggins, as loader of a gun, remained steadfast at his post throughout the furious 2-hour battle which resulted in the surrender of the rebel ram Tennessee and in the damaging and destruction of batteries at Fort Morgan.