Presently a line of bobbing objects caught his vision. Ordering the leading stoker to ease down the engines he signalled by means of hand-flags to the steamboat astern to likewise reduce speed.
The objects that had attracted his attention were the barrels forming the boom across the river almost abreast of the wrecked torpedo-station. The Pelikan, he knew, had been moored above the obstruction. She had drifted down past them before she took fire and blew up. Unless the boom had been temporarily removed and afterwards replaced he could not understand how the raider could have descended with the ebb-tide without sweeping the line of barrels away.
"What's wrong?" enquired Bourne.
Briefly Denbigh explained.
"It would be as well if we sent a shell into one of those barrels," he added.
"Waste of good ammunition," objected the lieutenant-commander. "The steamboat can take it bows on at full speed ahead. She'll do it easily."
"That I do not doubt," replied the sub. "But I have an idea that those barricoes are filled with explosives, although we bumped into one of them when we were in a light punt."
Just then the P.O. telegraphist for wireless duties, who was ensconced in a small insulated cage on the rearmost cutter, received a message from one of the sea-planes to the effect that the Germans had been located. They had landed from the boats at a spot twenty miles above the former anchorage of the Pelikan and were making their way towards the hills.
"They're funking it," declared Bourne. "Everything points to a hurried flight. They may have swung the boom back in position, but I doubt the accuracy of your mine theory."
"Very good, sir," replied Denbigh. "Then you wish the steamboat to charge the obstruction?"