In a general way it will probably be found possible to keep the boat on an even keel by means of her rudders, but if she shows any decided tendency either to dive to the bottom or to rise to the surface or to heel over to one side water may be admitted into the above-mentioned tanks, and the admission may be effected either automatically or by hand. A hydrostatic valve will prevent the vessel passing the safe limit of depth. _Air Supply and Ventilation._—Compressed air is stored aboard the vessel with means of allowing a supply of air into the interior of the vessel. Ventilators are provided for the circulation of outside air throughout the vessel; the gasoline vapours from the engines and all noxious gases are carefully excluded by suitable devices, while safety valves are provided to prevent the pressure to the vessel from exceeding that of the atmosphere. _Pumps and Pumping._—All tanks and compartments are connected with the pumps, the valves are located to allow of quick manipulation, and pumps with independent means of operation are furnished in duplicate. The tanks can also be emptied by flowing out. _Navigating Apparatus._—In communication with the interior of the vessel there are bells and speaking tubes, while there are provided gauges, indices, and clinometers for indicating pressure, depth, positions, quantities, and weights. Two compasses are carried, each compensated and adjusted. It is said that the first of the British submarines exhibited certain defects in its compasses, which it was thought were due to the steel conning tower. This was replaced by a brass construction, and on being tested the compasses acted more satisfactorily. After a few trials a new steering-wheel was fixed in the boat close to the conning tower, which could be worked from above and below alike. The first British submarine was launched on November 2, 1901, at Barrow without any ceremony, although representatives of the Admiralty were present. The trials were placed under the direction of Captain R. H. S. Bacon, D.S.O. Before launching “No. 1” was by means of a floating dock placed on the gridiron. A crew of six men were put on board, and she was then hermetically sealed for three hours, air being supplied by compressed air cylinders. The trial was quite successful, and the men suffered no inconvenience. On her first “sea trial” “No. 1” started from the floating dock and proceeded along the Devonshire and Buccleuch docks and back to her moorings. On subsequent trials she attained a surface speed of 10 knots.