ate aiming over such distances and of
locating your hits so that they destroy the comparative small area of
the fort is got over by the use of aircraft, which fly above the fort,
note the hits, and signal the results.

Now, the Germans maintained that under these quite recently modified
conditions not even the best handled and heaviest gunned permanent
fort could hold out more than a few days. The French believed that it
could, and they trusted in the stopping power not only of individual
works (such as the fortress of Manonvilliers on the frontier), but
more especially of great rings of forts, such as surround Liege,
Namur, Verdun, etc., and enclose an area within the security of which
large bodies of troops can be held ready, armies which no one would
dare to leave behind them without having first reduced them to
surrender.

The very first days of the war proved that the German theory was right
and the French wrong. The French theory, upon which such enormous
funds had been expended, had been perfectly right until within quite
recent years the conditions had changed. Port Arthur, for instance,
only ten years ago, could hold out for months and months. In this war
no individual fort has held out for more than eleven days.

It might be imagined under such circumstances that the very existence
of fortresses was doomed; yet we note that Verdun continues to make a
big bulge in the German line four months after the first shots fell on
its forts, and that the Germans are actively restoring the great
Belgian rings they have captured at Liege, Antwerp, and Namur.

Why is this? It is because another German theory has proved right in
practice.

III. This German theory which has proved right in practice is what may
be called "the mobile defence of a fortress." It proposes no longer to
defend upon expensive permanent works precisely located upon the map,
but upon a number of improvised batteries in which heavy guns can move
somewhat behind field-works concealed as much as possible, numerous
and constructed rapidly under the conditions of the campaign. Such
works dotted round the area you desire to defend are quite a different
thing to reduce from isolated, restricted, permanent forts. In the
first place, the enemy does not know where they are; in the second
place, you can make new ones at short notice; in the third place, if a
howitzer does spot your heavy gun, you can move it or its neighbours
to a new position; in the fourt