On board the USS Brooklyn during action against rebel forts and gunboats and with the ram Tennessee, in Mobile Bay, 5 August 1864. Despite severe damage to his ship and the loss of several men on board as enemy fire raked her decks from stem to stern, Irwin fought his gun with skill and courage throughout the furious battle which resulted in the surrender of the prize rebel ram Tennessee and in the damaging and destruction of batteries at Fort Morgan.