Failure of rollers was succeeded by failure of sprockets. Sprockets and rollers were hardly cured when the Germans produced a very reliable armour-piercing bullet. This after a very short innings was defeated by the arrival of the Mark IV. Tank. The Mark IV. Tank was barely rescued from the mud of Flanders by the invention of the unditching beam, when we discovered that the Hindenburg trenches were about one foot too wide to cross without some form of help to the Tank. This difficulty was overcome, but about this time the effect of concentrated machine-gun fire upon Mark IV. Tanks must have become known to the Germans, as also their vulnerability to the ordinary field gun. The position with regard to both splash and casualties from guns firing over the sights, was becoming serious when the arrival of Mark V. Tank, with its increased handiness and speed, put an end to the splash difficulty for ever, and defeated the field gun for a good long time. So on to the last days of the war, when we were able to look forward to 1919 with a certain knowledge that we had much in hand against any measure of opposition--short of a superior Tank--that the enemy could produce. The idea undoubtedly exists still in the minds of certain people that the particular form of Tank which they have seen or fought with represents the latest word in design. It does not. The latest Tank produced in any bulk was the type that marched through London on July 19. It has never fought, and it represents the last word only of the elementary series of Tanks of which Mark I. was the original. * * * * * If finality in design has by no means been approached in the war, the same may be said as regards the employment of the then existing types. This depended, after due consideration of their limitations and powers, on the training of personnel, not only of the Tank Corps, but essentially of infantry too. Lack of time, lack of opportunity, and wastage of trained personnel were the great difficulties which confronted commanders of every arm and formation in their efforts to reach even average standards of skill in only a few of the commoner phases of warfare. With the Tank Corps the additional difficulties of mechanical training were no more than balanced by freedom from the trench routine of troops employed for defence. For the infantry Tank, the training of Tank personnel alone is not sufficient. In the assault, Tanks are no more than a part of infantry, an integral part of the _troupes d’assaut_. For real success, i.e., cheap success, not only must the two arms train and re-train together, but they should live together, feed together, and drink together.