Lashed across the bows of the picquet-boat was a nun-buoy roughly three feet in diameter and four betwixt apex and apex. To the lowermost ring of the buoy, which was painted in red, white, and blue horizontal bands, was shackled fifty fathoms of light chain. At the other end of the chain was a "span" of heavier cable, each arm terminating in a fifty-six pound mushroom anchor.
A quarter of a mile to the nor'east'ard a Dutch cruiser was forging slowly through the water, her officers critically interested in the work of the British picquet-boats. The German batteries had refrained from opening fire, possibly on account of the proximity of the neutral cruiser, although it afterwards transpired that there was quite another reason for their passivity.
Keeping his picquet-boat running dead slow, bows on to the tide, so that the little craft was practically stationary over the ground, Tressidar determined his position.
"That's about it, sir, I think," he called out, addressing the senior officer, who was in another steamboat a short distance away.
"Near enough," replied the lieutenant. "At all events, I don't suppose the Dutchmen will quibble over it."
"Stand by to let go!" ordered the sub., speaking to the seamen for'ard. "Lower away roundly."
Mushroom anchor No. 1 disappeared with a splash, and having made sure that it was holding, Tressidar ordered easy ahead so as to drop the second anchor well clear of the former.
"Let go!"
The second anchor clattered overboard, taking with it the length of chain and the nun-buoy. Then, to the sub.'s surprise, the buoy, instead of floating sedately upon the surface, began to move rapidly through the water, impelled by some unseen force. So great was the rate of progress that the buoy frequently dragged beneath the surface, leaving a tell-tale swirl in its wake. Its direction was roughly south-west, which meant that it was being dragged away from neutral waters.
In a trice Tressidar grasped the situation.