Within a quarter of an hour of its leaving the cave the Zeppelin returned to earth. Anchored fore and aft it strained and staggered in the still strong wind. The officers and crew descended by means of a rope ladder, then the holding ropes were cast off and the aircraft bounded upwards. Hamerton could see that it was still connected with the ground by a flexible steel rope. The propellers were revolving and the rudders set hard over, consequently the Zeppelin was describing circles in the air at a height of a little over five hundred feet.
The words were hardly out of his mouth when the sharp, rapid detonations of a pom-pom were heard. Almost simultaneously with the screech of the projectiles sinister dark marks appeared on the aluminium cover of the Zeppelin; yet to the Sub's surprise the one-pounder shells without exception did not burst, neither did the airship appear to lose its reserve of buoyancy.
For nearly fifteen seconds the firing continued. Nearly four times that number of projectiles had been fired, many of the shot-holes overlapping each other.
Upon the conclusion of this severe test the Zeppelin was brought down, and, controlled by about fifty men holding guide ropes, was taken down the incline.
As it neared the turntable Hamerton was able to come to some conclusion as to the nature of the self-closing material surrounding the ballonettes. In one place the havoc wrought by the concentration of several projectiles had completely torn off a strip of aluminium measuring roughly two feet six inches by two feet. Within the cavity could be seen the inner lining of aluminium, which had been badly perforated, thus releasing all the hydrogen from that particular ballonette. At the edges of the perforations a substance resembling dirty cotton waste had been forced out. Only the width of the fissure prevented the closing up of the textile fabric.
As the Zeppelin was being guided on to the turntable a fragment of the plugging material fluttered to the ground. A breeze caught it and swept it towards the edge of the turntable pit. There it stopped, provokingly out of reach even if the Sub had dared to stretch out his hand to grasp it.
Just then one of the sailors manning the trail ropes kicked the piece of packing. It fell literally into Hamerton's hands.