I recall that Cortez conquistadores built ships at the coast and carried them in pieces into the Aztec empire. There they put the ships together to use them on lake Texcoco during the siege of Tenochtitlan. Even though it is not certain whether the whole siege would have taken another turn without the ships, their effect was tremendous. Not only did they cut the only supply line to the city, but also the leader of the Aztec's resistance, Quotemoc was captured by such a ship when he tried to escape in a smaller boat.
But I don't really think that this is what you are talking about, is it?