The command is then given: "Fill main ballast!" Quick-opening valves are opened and the water rushes into the ballast tanks and superstructure at the rate of fifty or sixty tons per minute. The order is then given: "Trim for submergence!" Sufficient water is then admitted into the final adjustment and trim tank to give the desired buoyancy and trim, and the vessel is now ready to submerge on signal from the commander, who now takes his station at the periscope. The gunners have also taken their stations at the torpedo tubes to prepare to load the tubes as soon as the torpedoes already in the tubes are discharged. The whole time consumed from the time word to "prepare to submerge" until the vessel is running under water has probably not been over two or three minutes. In the meantime the enemy has been rapidly approaching and her superstructure is already above the horizon. The commander of the submarine notes that if the enemy holds its course it will be advantageous to change his position to intercept the oncoming fleet. He therefore gives word to submerge to the desired depth and gives the quartermaster the course, and the vessel proceeds, entirely submerged, to get nearer the enemy's line of approach. The commander then brings his submarine to rest before extending his periscope above the surface. As soon as the enemy is found to be coming within range he manoeuvres his ship so that his torpedoes will bear the proper distance in advance of the ship he selects to destroy. To make a hit it is necessary to fire in advance of the oncoming ship to allow for the time the torpedo takes to reach the point where the enemy will be. Range finders, torpedo directors, and rapid calculators enable the commander to calculate this to a nicety. If the distance is only a thousand or fifteen hundred yards, a hit is pretty certain to be made, but the greater the distance the less the chance of success and the greater the opportunity for error. CHAPTER II COMEDY AND TRAGEDY IN SUBMARINE DEVELOPMENT One of the first queries which laymen usually direct at the submarine navigator is, "Are you not afraid that the boat will never come up?" and other variants on the same theme. Most people are surprised and many are very sceptical when they are informed that there is no sensation at all connected with the act of going under water in a boat except that due to one's own imagination. The fact is that if one were going down inside the vessel in some of the modern submarines he could not readily tell whether the vessel was running on the surface or navigating in a submerged condition.