As seaman on board the USS Metacomet, Johnson served as a member of the boat’s crew which went to the rescue of the U.S. Monitor Tecumseh when that vessel was struck by a torpedo in passing the enemy forts in Mobile Bay, 5 August 1864. He braved the enemy fire which was said by the admiral to be “one of the most galling” he had ever seen, and aided in rescuing from death 10 of the crew of the Tecumseh, thereby eliciting the admiration of both friend and foe.