It was not until an hour after sunset that the welcome order came to blow auxiliary tanks. Without making use of her propelling machinery the submarine rose steadily towards the surface. Everything seemed quiet. The periscopes, useless except for the purpose of picking up a solitary light, revealed nothing, for the night was already as black as pitch.
With their night-glasses the officers swept the waste of waters. Ahead a faint "loom" indicated the position of Copenhagen. On the Swedish side a faint light flickered for a few seconds and then disappeared.
A quarter of an hour passed, but Stockdale gave no orders to proceed. Not that he hesitated to face the danger; he was merely waiting an opportunity.
Suddenly the horizon away to the south'ard was swept by the rays of a search-light. Another and yet another beam followed suit, until the sky in that direction was a blaze of light. Then the rays vanished and a mast-head signalling-lamp began its flickering tale.
"'QKG—TOXZ—PJ'—code, thought so," muttered the Lieutenant-Commander, as he read the unintelligible message.
"Mast-head signal astern, sir," reported Fordyce.
The Hon. Derek swung round in an instant and levelled his binoculars at a pin-prick of yellow light.
"Good!" he ejaculated. "That's what I was waiting for."