"All secure!" he spluttered. "Let's hope the buoy won't bump before we're well away. Strike out, Peter."
Both swam their hardest. Breathlessly they clambered over the yacht's side, and without loss of time the Puffin gathered way and drew clear of the danger zone. Peter and his Scoutmaster went below to dress.
As soon as possible they regained the cockpit. Brandon was keeping the yacht tacking at about a quarter of a mile from the square of red bunting that indicated the position of the now invisible menace.
"Now for a little signal-practice," said Mr. Grant briskly. "Where's the Code Book. Let's hope our letter B won't be required."
The Puffin was within visual signalling distance of Dungale coastguard station. Her signal, reporting the presence of a floating mine was seen and acknowledged.
"We may as well hang on and see the fun," observed Mr. Grant, and the suggestion met with unanimous approval.
Within half-an-hour the fishery protection gunboat appeared upon the scene, and the highly interested Sea Scouts watched the proceedings with zest.
The gunboat opened fire with rifles and a machine-gun. The red signal flag disappeared as if by magic. All around the spot the water was churned by the hail of bullets. Yet the mine did not explode.
"Probably a dud," commented Brandon when the firing ceased. "They've sunk it, more than likely."
But after a brief interval the gunboat reopened fire. Suddenly a huge column of water was flung high in the air, to be followed almost immediately by the terrific crash of the explosion.