1774, a Spanish 25m sailing ship appeared, and people canoed out to it, but a wind blew the ship away. 4 years later the Spanish met the Nuu-chah-nulth, and began trading sea otter, which spread along the west coast. Because pelts only lasted a few years, demand was extreme, and by 1820, the once numerous animals were becoming hard to find. The Haida made peaceful contact, but only to a certain extent. They added sails and swivel guns to their canoes, and sunk many European ships. They then pillaged the ships, using stolen cannons to their advantage. As early as 1795, a British trading ship fired its cannons at a village in the central part of the archipelago because some of the crew had been killed by the inhabitants, and the survivors had to put hastily to sea when the Indians fired back at them. They found out later that the Indians had used a cannon and ammunition pilfered from an American Schooner a few years earlier. Even swivel guns were mounted on war canoes Fortified sites were used by all Northwest Coast groups for at least 2,000 years. Military defences at Haida forts included stout palisades, rolling top-log defences, heavy trapdoors and fighting platforms supplied with stores of large boulders to hurl at invaders.