"That means a heavy loss of life."
"A terrible loss of life," the master agreed. "Moreover, even should they advance in such masses that we could not kill them fast enough and thus they should storm the slope and win the ditch, they would be in a still worse plight. Powerful quick-firing guns, mounted in cupolas at each angle of the triangle, sweep the sunken ditch with an enfilading fire. No troops could live through such an inferno of bullets.
"On the main inner triangle is the infantry parapet, shaped somewhat like a heart, pierced for rifle fire and with machine-gun emplacements at the angles. In the hollow of that heart-like space rises a solid central mass of concrete, on and in which are the shelters and gun cupolas. The mortar cupolas rise from the floor of the hollow, outside the central mass. These are invisible to the foe until raised by machinery within, when they command the entire neighborhood and can fire their 6-inch shells in any direction."
The doctor rubbed his hands briskly.
"If that's the way our forts are built," he said, "and if they are well provisioned and have plenty of ammunition, we ought to be able to snap our fingers at the Kaiser. All we have to do is to wait for the Germans to come and shoot them down by thousands. They'll go packing back to Germany quick enough if we give them a reception like that."
"Perhaps," said the old reservist, "but you have forgotten about the howitzers."
"Why, yes, so I had," the doctor answered, more gravely; "you were going to tell me about them."
"The difference in principle between a gun and a howitzer or a mortar," explained the master, "is that a gun depends for its destructiveness on its striking velocity, while a howitzer depends on the power of the exploding charge of its shell. An armor-piercing shell, fired from a 15-inch naval gun, will go through the heaviest and hardest steel known, because of the terrific speed at which it travels, with a muzzle velocity of three thousand feet a second or thirty-four miles a minute. In order not to lose speed, therefore, it must travel in as straight a line as possible. In other words, a missile from a gun must have a long low curve or trajectory."
"Yes," said the doctor, "I can see that."
"A howitzer, on the other hand," the master explained, "does not require any more velocity than just to carry the high-explosive shell to the point designed. Moreover, in order that their terrible effects may be the more destructive, mortars and howitzers drop their shells from overhead upon the object of fire by lobbing them up in the air with a very high trajectory. A howitzer generally looks as though it were shooting at the moon. It can be placed in a valley and fire over the hill. But, as you can see, its range is restricted. A naval gun throwing an 8-inch shell may have a range of sixteen miles, while the 8-inch howitzer operates best from three or four miles away.