In Long Island Sound we found, during a deep submergence trial with one of our submarines, a depth of two hundred and fifty-six feet, whereas the chart indicated a depth of only twenty-seven fathoms (one hundred and sixty-two feet). In one instance in Russia we were conducting submerged trials on the official trial course of the Russian Government in the Gulf of Finland, this being the course on which they tried their surface torpedo boats, and we were assured that there was not less than sixty feet of water on the course, yet we struck rock peaks twice on this course in less than thirty feet depth. The record of ships that have been lost, due to striking uncharted rocks and shoals, is a large one, and a more correct topography of the water-beds of our coast and inland waterways should be worked out. In 1899 and 1901 considerable time was spent in experimental work with the submarine boat _Argonaut_ in locating sunken ships and recovering their cargoes. To find a sunken ship it was necessary to search the bottom thoroughly, and many experiments were made and success attained to such an extent that we could search thoroughly an under-water area of from ten to twenty square miles per day. It is the result of this experimental work that has led to the design of the herein-described apparatus, which will give very accurate contour records of the bottom within such depths as would prove of interest to navigators of either surface vessels or submarines. The advent of the submarine has made it more important to know where obstructions exist, as they require at least seventy feet depth to navigate at speed entirely submerged and to enable them to keep below the bottom of surface ships. This method of water-bed surveying consists of using two or more submarine boats of my bottom-navigating type, with access tubes extending to surface vessels. Instead of using two bottom wheels arranged in tandem, as is used on my military submarine, I use a single pair of toothed driving wheels capable of being swivelled and driven to propel the submarine in any desired direction over the bottom. The submarine vessel contains also a diver's compartment, so that examinations of the bottom may be made and a record kept of the materials and conditions found, which are recorded as frequently as may be desired directly on the contour sheet, on which the soundings are being automatically recorded.