"They were when they were built," the master answered, "but that is twenty years ago. Against the guns of that period, notably the 6-inch howitzer, they were impregnable, for every possible gun-position for a weapon of that range was covered by the guns of the fort. But if pieces of heavier power can bombard the forts from positions outside the range of the fortress guns, then impregnability is gone. You must remember, Doctor, that the power of a gun increases as the cube of its caliber or diameter of its bore. Thus a 12-inch gun is not twice as powerful as a 6-inch gun, but eight times as powerful."
"Are there such heavy guns?"
"There are," was the answer. "Field guns of 8.4-inch and 10-inch caliber are known to exist, and the German War Party is reported to hold the secret of still more powerful engines of destruction, of which, as yet, the outer world knows nothing."
"Look, you, M. Maubin," said the surgeon, "you seem to know quite a lot about these things, while I've concerned myself mainly with my medical books and haven't paid much attention to military affairs. Explain to me, if you will be so good, the significance of this contest between the fortifications of Liége and the new German guns."
"It is the death-grapple which will decide the fate of Belgium—perhaps that of Europe—within a week," the master answered. "Its outcome will settle the greatest military controversy of our times. One way or the other, it will change the face of war forever. This question is whether modern artillery has become so powerful that no permanent masonry fortification can resist it. If so, the development of two thousand years of fortification must be thrown aside as useless and defense must become mobile.
"Liége is what is known as a ring fortress, that is, the city itself is not fortified but it is ringed round with twelve forts, between two and three miles apart from each other and averaging a distance of five miles from the city. Thus the forts form a circumference of 32 miles, so arranged that if any one fort is silenced the cross-fire of the forts on either side controls the gap. Six are forts of the first order, Pontisse, Barchon, and Fléron on the north and east, Loncin, Flemalles, and Boncelles on the west and south. The other six are fortins or small forts, like Embourg."
"Are they strongly armed?" the doctor asked.
"Moderately so. They have modern guns, though not of the largest caliber. There are four hundred guns in all the forts combined, mainly 6-inch and 4.7-inch guns and 8-inch mortars. The big 9-inch guns, which were ordered from Krupp's for delivery more than three years ago, have never reached us. We see, now, that Germany would not allow them to be delivered. She did not intend to run the risk of invading a well-armed Belgium."
"But isn't a 6-inch a fairly big gun?"
"Not for permanent works," the master replied. "The United States has two 16-inch guns in her coast defenses and there are plenty of 12-inch guns in permanent fortifications. Naval guns, of course, are bigger. They have to be. You can't 'take cover' at sea and long ranges therefore are necessary. Modern super-Dreadnoughts,[3] armed with 15-inch guns, regard their 6-inch batteries as merely secondary.