At a rate approaching one hundred and eighty miles an hour the battleplane was soon out of sight of land. She had at first held a north-westerly course in order to avoid passing over Libau, then in the possession of the Germans. Blake, although he would not have declined another aerial fight, was anxious to traverse the Baltic before the Huns were aware that he had left the Russian frontier. There was work awaiting the battleplane in France—work of far more importance than engaging individual hostile seaplanes in the neighbourhood of the Cattegat.
Fifty minutes after leaving Riga the Swedish island of Gothland was sighted. At this point the course was altered to the south-west, until the island of Bornholm was discerned.
Although numerous Russian warships and patrol-boats had been sighted at the entrance to the Gulf of Riga the Baltic was almost deserted, except towards the Swedish shore, where several enemy merchantmen were hugging the coast in order to avoid the studied attentions of the British and Russian submarines. But of German warships there was no sign.
Presently Blake's trained ear caught a disconcerting sound that was repeated time after time with increasing frequency. Dick, sliding from his seat, made his way to the motor-room; then, after a brief examination, approached his chief.
"She's firing badly," said Blake gravely.
"Yes," assented Dick. "It's not the ignition this time. It's the petrol. It is my belief that either the stuff is very inferior or else that it has been watered. Whatever it is the rotten stuff is now passing through the carburettors. Hitherto we've been running on the petrol we brought with us."
"Was it strained?" asked Blake anxiously.
"I stood by and saw it done," reported Dick. "Of course some one might have tampered with the tanks during the night. There are spies with the Russian troops as well as there are in the French and ours, worse luck. There she goes again," he added, as the motors faltered badly for several strokes and then spasmodically fired again. "Ought we to turn back?"
"I don't believe in turning back," said the inventor. "No, the sea is calm, there are no vessels in sight. We'll volplane down, rest on the surface and re-strain every drop of petrol on board."
Preparations were quickly made for the venturesome enterprise. The hatchway in the floor of the fuselage, which was already shut, was now hermetically sealed by means of wing-nuts that jammed the metal flap hard down upon an indiarubber seating. A similar watertight covering closed the aperture through which the bombs were dropped in action. The exhaust, which generally led through a pipe on the underside of the rear part of the chassis, was diverted by means of a two-way union so that the former escaped from an outlet and projecting well above the deck. Thus, in less than five minutes the hull of the battleplane was made absolutely watertight and ready to float upon the waves.