The date is Sept. 6, 1776. In New York Harbor near midnight, an Army Sgt. (yes, Army) crept out of a small rowboat into an egg-shaped wooden vessel and fastened the hatch over his head. For the first time in the history of naval warfare, an enemy ship was about to be attacked by a submarine -- in this case, two shell-shaped wooden halves fastened together with iron bands and covered completely with a thick coating of waterproof pitch. Although the attack that night against England's HMS Eagle was unsuccessful, the pilot of the Turtle, which was built in Old Saybrook by David Bushnell, did manage to release and detonate the torpedo he was carrying in open waters, which served to unnerve the British fleet so much that they immediately pulled out of New York Harbor (adapted from http://www.military.com/Content/MoreContent?file=ML_elee_bkp).
After finding the cache, visit the nearby grave of Sgt. Ezra Lee (N 41 18.627, W 072 19.660) and pay your respects to America’s First Submariner. His is the only veteran's stone that states he "was esteemed by Washington". If you want to see a full-scale replica of the Turtle, visit the Connecticut River Museum in Essex.