1761 of my British campaign. Started negotiating with my Polish allies to see if they had any useful techs to trade and I find that I can offer:

"Underhand Submersible Warfare:
When conventional warfare at sea fails to destroy the enemy, perhaps it is time to consider the unconventional schemes of inventive madmen"!

Pretty damn sure I haven't researched this, and can't find it on the research screen.

Anyone else seen this or is it something that another faction can get (only played Brits so far)? I believe that the US experimented with prototype sub technology in this time period, is it in the US tech tree?

(How do I post screenshots?)