The USS Constitution, nicknamed Old Ironsides, is a wooden-hulled, three-masted heavy frigate of the United States Navy. Named by PresidentGeorge Washington after the Constitution of the United States of America, she is the world's oldest commissioned naval vessel afloat. Launched in 1797, Constitution was one of six original frigates authorized for construction by the Naval Act of 1794 and the third constructed. Joshua Humphreys designed the frigates to be the young Navy's capital ships, and so Constitution and her sisters were larger and more heavily armed and built than standard frigates of the period.
While in Boston to receive the plutonium from HMS Sea Nymph, Leslie Groves saw the Constitution, still berthed in the Navy Yard. During his time at MIT, he'd toured the ship several times, and it always gave him a thrill seeing the ship.