The Turtle was an actual submersible vehicle used against the British in the Revolutionary War. It was made in the USA in 1775 and was unsuccessful in sinking any British ships.
During the final scene with Robert Rogers, he refers to the British officer as a "pissant" a term not coined until 1935.
In the episode the Turtle is depicted as being in storage in Morristown, New Jersey as of winter 1778. The actual Turtle was used in one attempted attack on a British warship on September 7, 1776, and is believed to have been destroyed during autumn 1776 to prevent its capture by the British.