Then, firing torpedoes is not at all like firing big guns. At a range of five miles a shell will still be making 2000 feet a second or 1400 miles an hour. At the same range a torpedo like those used at Jutland would be making only 50 feet a second or 35 miles an hour. Thus shells whizz through the air forty times faster than torpedoes sneak through the water. A torpedo, in fact, is itself very like a submarine, more or less cigar-shaped, and with its own engine, screw, and rudder. Hitting with a torpedo really means arranging a collision between it and the ship you are aiming at. When you and the ship and your torpedo and the water are all moving in different ways you can see that hitting is not so easy. The shorter the range the better. But you cannot see at all unless your periscope, with its little mirror, is high and dry out of the water; and periscopes are soon spotted by a sharp look-out at very short range. The best torpedoes are over twenty feet long and as many inches through, and they will go ten miles. But the longer the range the slower the pace and the less the chance of hitting. The engine is driven by air, which is compressed so hard into the middle of the torpedo that it actually bulges out the steel a tiny fraction of an inch. You may set the air-valve fast or slow, and the torpedo will go accordingly. But if you want to make pretty sure you must get within less than a mile, with the ship's broadside toward you, set the torpedo for the right depth, the right pace to keep it going as fast as possible just long enough to hit, and of course the right aim. Then, if all goes well, the cap, or "war head" of the torpedo, on hitting the ship, will set off the fuse that sets off the tremendous charge of high explosive; and this may knock a hole in the side big enough to drive a street car through. But there are many more misses than hits. Yet the German and Austrian raiders, mines, and submarines sank fifteen million tons of shipping, which is not far short of a third of all the merchant tonnage in the world; and the submarines sank more than the mines and raiders sank together. (Ships are measured by finding out how many cubic feet of space they contain and counting so many feet to the ton. Thus you get a much better idea of how much shipping a country has by counting in tons rather than by the number of ships; for twenty-five ships of one thousand tons each have only half as much sea-power as one ship of fifty thousand tons.) The British loss was nine millions, half as much again as was lost by all the rest of the world put together. Raiders like the cruiser _Emden_, or the armed and disguised merchant vessel _Möwe_, did a great deal of harm at the beginning of the war, as we have seen already. Mines did even more harm, and did it all through. But submarines did most.