Actual trials of the pontoons and their monitor escorts were made in the secret waters of the Thames, and officers of the Tank Corps would suddenly disappear on unknown missions, to reappear as suddenly with no memory as to where they had been or what they had seen in the interval. The sea wall itself might well have been designed as a special defence against sea-borne hostile Tanks, its smooth concave face and projecting coping making it absolutely unscalable by an honest Tank. The wall was of recent construction, and by a fortunate chance the Belgian architect who had designed it had escaped to France with all his drawings. From his plans an exact reproduction of a length of the wall was made. There in the experimental ground it stood, perfectly smooth, and worst of all, ending at the top in a curl-over coping. At least, however, the engineers now knew the extent of their problem. In the first place, the Tanks had to get up somehow, and in the second place, when they were up they had to help haul up guns and transport lorries. After “trying on” various devices, the Tanks at last adopted what was practically a portable ramp for the occasion. The Tank, until it reached the sea wall, carried it well in the air on a long spar supported by wire hawsers. Then the ramp was lowered on to the pair of little wheels with which it was fitted. On these the Tank pushed it up the incline, wheelbarrow fashion, until further progress was stopped by the coping. The two wheels were then immediately shed, and steel spikes on the under side of the work were driven into the concrete by the weight of the Tank, which now, disengaging itself, proceeded to climb up its own scaling ladder which it had thus placed in position. But the lorries and guns had still to be provided for. The angle formed by the inclined plane and the level ground above the retaining wall was a sharp one. Besides, it must be understood that the inclined plane used by the Tanks fitted in under the concrete lip. At the point of junction between the ground and the inclined plane there was, therefore, a considerable bump. Both the acuteness of the angle and this “bump” made it necessary to adopt some less back-breaking device for the four-wheeled vehicles. A strong gangway, like a see-saw, was therefore employed, and up this they were hauled, the weight of the gun or lorry gently tipping the board down when it passed the balancing point. But the landing was never made, and for this many elaborate explanations have been put forward. Two circumstances seem, however, sufficient to explain the apparent withdrawal of our hands from the plough. The first was what seemed a trivial attack which the Germans made on July 10.