Everything connected with the kite-balloon presented more or less of a problem because it was new. The mobile windlass, for example, by which the balloon was let up and pulled down on its cable, had to be developed from nothing. But the genius of the American manufacturer overcame this difficulty as it did every other in the manufacture of instruments for war. Though steam was the motive power first used for balloon windlasses, before the close of the war American ingenuity had developed both gas and electric windlasses which were thoroughly efficient. The mobile windlass could move on the road under its own power at a speed of twenty miles an hour, and could tow a balloon in the air at the rate of five miles an hour, or even better if necessity demanded. The gasoline windlass has made a record pull-down of 1,600 feet a minute, bringing down its balloon at a speed more than _three times that of the fastest passenger-elevator_. A sufficient supply of hydrogen gas was, at the beginning, another of the balloon problems. Hydrogen, before the war, was a by-product in the manufacture of commercial oxygen, and only a small quantity was used in this country. But the sudden demand for millions of cubic feet of this gas was promptly met by the establishment of government plants and the expansion of privately owned ones. Though by far the greater part of the gas used in balloons at home and abroad was made at permanent supply stations and shipped to the points where it was needed, in steel cylinders, an extremely ingenious type of portable generator was developed for the manufacture of hydrogen in the field. When these portable hydrogen generators were unnecessary or unavailable, the gas shipped from long distances was stored in high-pressure cylinders or “nurse balloons,” the latter being simply huge bags of rubberized fabric, each with a capacity of 5,000 cubic feet of hydrogen, which were used in the same way as the ordinary steel gasometers to be seen in any American city.