Born in 1826 in Charlestown, Massachusetts, Dennis was living in Boston when he joined the Navy. He served during the Civil War as a boatswain's mate on the USS Brooklyn. At the Battle of Mobile Bay on August 5, 1864, he operated the ship's torpedo catcher (an early naval minesweeping device). He helped fire the bow chase gun during heavy fire. Because of this action, he was given the Medal of Honor four months later, on December 31, 1864.[1][2]
Dennis's official Medal of Honor citation reads:
On board the U.S.S. Brooklyn during successful attacks against Fort Morgan, rebel gunboats and the ram Tennessee in Mobile Bay, on 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, Dennis displayed outstanding skill and courage in operating the torpedo catcher and in assisting in working the bow chasers 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.[2]
