The hull of the _Turtle_ was not made of copper, as is sometimes stated, but was “built of oak, in the strongest manner possible, corked and tarred.”[5] The conning-tower was of brass and also served as a hatch-cover. The hatchway was barely big enough for the one man who made up the entire crew to squeeze through. Once inside, the operator could screw the cover down tight, and look out through “three round doors, one directly in front and one on each side, large enough to put the hand through. When open they admitted fresh air.” On top of the conning-tower were two air-pipes “so constructed that they shut themselves whenever the water rose near their tops, so that no water could enter through them and opened themselves immediately after they rose above the water. “The vessel was chiefly ballasted with lead fixed to its bottom; when this was not sufficient a quantity was placed within, more or less according to the weight of the operator; its ballast made it so stiff that there was no danger of oversetting. The vessel, with all its appendages and the operator, was of sufficient weight to settle it very low in the water. About 200 lb. of lead at the bottom for ballast could be let down 40 or 50 feet below the vessel; this enabled the operator to rise instantly to the surface of the water in case of accident.” The operator sat on an oaken brace that kept the two sides of the boat from being crushed in by the water-pressure, and did things with his hands and feet. He must have been as busy as a cathedral organist on Easter morning. With one foot he opened a brass valve that let water into the ballast tanks, with the other he worked a force pump to drive it out. When he had reached an approximate equilibrium, he could move the submarine up or down, or hold it at any desired depth, by cranking a small vertical-acting propellor placed just forward of the conning-tower on the deck above. Before him was the crank of another propellor, or rather tractor, for it drew, not pushed, the vessel forward. Behind him was the rudder, which the operator controlled with a long curved tiller stuck under one arm. [Illustration: The Best-known Picture of Bushnell’s _Turtle_. Drawn by Lieutenant F. M. Barber, U. S. N., in 1875.] Bushnell, in his letter to Jefferson, calls each of these propellors “an oar, formed upon the principle of the screw,” and the best-known picture of the _Turtle_ shows a bearded gentleman in nineteenth-century clothes boring his way through the water with two big gimlets. But Sergeant Ezra Lee of the Connecticut Line, who did the actual operating, described the submarine’s forward propellor (he makes no mention of the other) as having two wooden blades or “oars, of about 12 inches in length and 4 or 5 in width, shaped like the arms of a windmill.” Except in size, this device must have looked very much like the wooden-bladed tractor of a modern aeroplane.