Owing to its ceiling, rate of climb and speed, which we take to be from 70 to 80 miles per hour in the airship of the future, the airship may be regarded as comparatively safe against attack from the ordinary type of seaplane. The chief danger to be apprehended is attack from small scouting seaplanes, possessing great speed and the power to climb to a great height, or from aeroplanes launched from the decks of ships. If, however, the airship is fitted to carry several small scout aeroplanes of high efficiency in the manner described in the previous chapter, it will probably be able to defend itself sufficiently to enable it to climb to a great height and thus make good its escape. The airship, moreover, will be more or less immune from such dangers if the non-inflamable gas, known as "C" gas, becomes sufficiently cheap to be used for inflating airships. In the past the expense of this gas has rendered its use absolutely prohibitive, but it is believed that it can be produced in the United States for such a figure as will make it compare favourably with hydrogen. The navigation of an airship during these long voyages proposed will present no difficulty whatever. The airship, as opposed to the aeroplane, is reasonably steady in the air and the ordinary naval instruments can be used. In addition, "directional" wireless telegraphy will prove of immense assistance. The method at present in use is to call up simultaneously two land stations which, knowing their own distance apart, and reading the direction of the call, plot a triangle on a chart which fixes the position of the airship. This position is then transmitted by wireless to the airship. In the future the airship itself will carry its own directional apparatus, with which it will be able to judge the direction of a call received from a single land station and plot its own position on a chart.