Its nose could cut through them like the threads that they were. But the torn ends would catch conning tower and masts and periscope tubes. Even if it tore away from them, the whirl of the propellor remained to renew the danger, sucking the trailing cords to itself and in one instant switching them around and around the spinning shaft. With the propellor blocked, the submarine must rise; for only with its propellor thrusting and its horizontal fins set to hold it down, can the submarine stay under. It submerges, not by sinking but by diving with main strength. Another rather vivid picture flashed into the Lieutenant’s mind. It was not a picture, this time, of a wolf among sheep. It was a picture of a sudden enormous commotion among those quiet net-buoys, as of something struggling down below; and then of a violent surge as the tangled nets were dragged to and fro by a helpless submarine, held fast by the tail.[34] A breeze arose with the rising sun, and the water roughened. The submarine stopped. It could not meet rough water while it was awash. Although its buoyancy when it was sealed was such that its propellor had to thrust full speed to make it dive, yet with its hatches open two hundred gallons of water, far less than is contained in a single big wave, would send it down like a tin can.[35] The Commander held on as long as he could, watching the whitening water in the east, and watching the transports. He saw that at a thousand yards’ distance around them (just what he would have chosen as neat torpedo range), there lay a little fleet of gun-boats, all thrusting out booms with steel nets, that made them look oddly as if they were hooped and wide-skirted. Disposed in an oval, they guarded the transports with a second wall of steel wire. And overhead, soaring in spirals, never flying far away, and always returning, were three naval planes. The Commander of the M-9 knew that they were waiting and watching for just one thing--the “shadow” of a submerged submarine.[36] This enemy, plainly, was taking no chances. The fleet had power and time. It bent them to one object--to land its men safely. It would not engage the harbor defenses, and so open itself to the risks of plunging fire and torpedo attack. It would not blockade harbors, and so make itself a chosen mark for such terrors as M-9. _The Three Harbor Gates to New York and Boston_ Very scientifically, very thoughtfully, had the enemy staked out the vital spot at which he had decided to strike. Here, facing each to each almost like the salients of a fortification, lay three harbor gates to the northeastern United States--Buzzards Bay, gashing deeply into Massachusetts: Narragansett Bay, almost cutting Rhode Island in two: and the eastern entrance to Long Island Sound and the cities of Connecticut.[37] Open any one of these gates, and it opened the way at one blow to both New York and Boston.