We recovered a 1.37m destroyer hull at the base of a dam, 12m deep, but it was due to the fact that we had two qualified scuba divers on site. It had to be found using a no visiblity technique, where the diver spreads his arms out and swims brushing his arms and chest along the bottom of the pond. After the model was found, the diver said, " I used this technique, and had to hope I wasn't going to find a huge stump or log with my face."