Both Hun machines were now flying on a parallel course, the first one manoeuvring to return to the attack. Incautiously they were approaching the anchored U-boat.
Like an arrow from a bow, a gleaming steel cylinder leapt from the Q-boat's side. Striking the water with a shower of spray, it dived obliquely and made straight for the Hun's booby-trap, its trail clearly defined by the milky foam on the surface.
Suddenly there was a lurid flash that seemed to outshine the light of the sun. A roar so stupendous that it shook Q 171 from stem to stern gave warning that the torpedo had reached its mark.
The terrific crash was not merely the result of the torpedo detonating. Laden with tons of powerful explosive, the decoy U-boat was literally blown to fragments. Even at the intervening distance pieces of molten metal hit Q 171 with great force. Fragments rattled against her side and on her deck like hailstones upon a galvanised iron shed.
For a brief space officers and men were stupefied by the overpowering concussion. Wakefield and three of the seamen were hit by flying debris, although fortunately the wounds were nothing worse than skin deep. In fact, Wakefield, in the excitement of it all, was unaware of the fact until Meredith called his attention to a trickle of blood down his cheek.
The first seaplane, which at the moment of explosion was immediately above the anchored U-boat, had vanished utterly in the irresistible blast of fire. The other, with her wings and tail planes riddled and rent, fluttered downwards like a wounded bird until, the drop developing into a tail-spin, she crashed into the sea. Floats were shattered under the impact, and almost before the foam had subsided the wreck of the second seaplane had disappeared beneath the waves.
"The stunt's a wash-out," declared Morpeth disappointedly. "It might have been worse, though, if those seaplanes had brought a crowd of their pals with them instead of being too sure off their own bat. We'll have to leg it for home."
"If we can," added Wakefield calmly. "Look!"
He pointed with outstretched arm towards the south-west. Pelting along at high speed, with their funnels belching out clouds of oil-fed smoke, were seven German ocean-going torpedo boats. Simultaneously, away to the nor'ard, three more columns of smoke indicated pretty plainly that Fritz was doing his utmost to trap the too daring Q-boat.
"Tough Geordie" shrugged his massive shoulders.