Backwards and forwards he strove to move this object. It seemed immovable. He tugged, pushed, twisted it all to no purpose.
"Like everything else on board this blessed packet the thing's jammed," he growled. "I'll get a cold chisel from the armourer's chest and cut a hole through the plate. Great Christopher Columbus! what's that?"
A bell was ringing violently in some part of the aircraft. Perhaps, after all, there were more of the crew still at their posts on the upper platform?
He was about to descend, when, his eyes getting more accustomed to the gloom, he caught sight of a bolt placed at less than a foot from the knob that had so completely baffled his efforts.
He drew back the bolt. The flap above his head immediately swung back on a pivot, disclosing a long tunnel-like shaft. Simultaneously the bell ceased to ring.
"What a silly ass I am!" declared Hamerton. "I see the game. By touching that knob a bell rings for the purpose of warning those on deck that someone is ascending. That is quite feasible, since two persons could not pass each other in this exaggerated tin-whistle pipe."
Without hesitation he commenced to climb. The interior of the tube was of polished aluminium and reflected shafts of light that entered from the open top. He could see the blue sky overhead.
It was a long climb, for the vertical passage was nearly fifty feet in height. It reminded the Sub of the interior of a battleship's mast. A faint scent of hydrogen assailed his nostrils. Whether it was an accidental leakage sufficiently serious to affect the buoyancy of the airship or merely the natural wastage from the ballonettes the Sub knew not.
Upon gaining the upper platform Hamerton's first act was to inspect the fore-and-aft shelters. Both were deserted. They were also practically intact. The standard compass for'ard was in working order. More by force of habit than anything else he glanced at the card. The Zeppelin's bows were pointing due east--exactly the opposite direction to the way he wanted.
This was a most disconcerting discovery. To be ignominiously borne back into German territory was humiliating. Rather than let that happen he would attack the ballonettes, liberate the hydrogen, and allow the aircraft to settle, half-water-logged, on the North Sea.