Now the grades of warfare that have been developed since the present war began, may be regarded as a series of elaborations and counter elaborations of the problem which begins as a line of trenches behind wire, containing infantry with rifles and machine guns. Against this an infantry attack with bayonet, after shrapnel fails. This we will call Grade A. To this the offensive replies with improved artillery, and particularly with high explosive shell instead of shrapnel. By this the wire is blown away, the trench wrecked and the defender held down as the attack charges up. This is Grade B. But now appear the dug-out elaborating the trench and the defensive battery behind the trench. The defenders, under the preliminary bombardment, get into the dug-outs with their rifles and machine guns, and emerge as fresh as paint as the attack comes up. Obviously there is much scope for invention and contrivance in the dug-out as the reservoir of counter attacks. Its possibilities have been very ably exploited by the Germans. Also the defensive batteries behind, which have of course the exact range of the captured trench, concentrate on it and destroy the attack at the moment of victory. The trench falls back to its former holders under this fire and a counter attack. Check again for the offensive. Even if it can take, it cannot hold a position under these conditions. This we will call Grade A2; a revised and improved A. What is the retort from the opposite side? Obviously to enhance and extend the range of the preliminary bombardment behind the actual trench line, to destroy or block, if it can, the dug-outs and destroy or silence the counter offensive artillery. If it can do that, it can go on; otherwise Bloch wins.