The Capella was about to resume her course when a warning cry was heard:
"Torpedo coming, sir!"
From a point bearing half a mile on the vessel's port quarter, the track of the on-coming torpedo was clearly discernible. The Capella, being without way, would undoubtedly have fallen a victim had it not been for her light draught, for before she could forge ahead the missile passed under her keel. Its track could be followed as far as the eye could reach, which showed that it was a modern weapon propelled with superheated air and having a range of about five miles.
Straight for the source of the missile, tore the British craft, but her effort to grapple with the unterseeboot was in vain. The submarine had dived immediately. No sounds betrayed her presence in the vicinity. Had the U-boat been moving, the churning of her propellers would have been distinctly audible.
"She's got away, worse luck," growled Sub-lieutenant Fox. "I wonder how she did it? It's too deep for her to sound, and she can't be moving under her own power."
"We'll have her right enough," rejoined Barry, the optimist. "A light haze and a calm sea is what we want. We'll run her down in less than a week, you mark my words."
Four days passed. The Capella kept her station almost without incident. Ship after ship, deeply laden with troops and munitions, entered the sand-banked estuary of the Seine, having been escorted thus far by destroyers. Ship after ship, more lightly burdened, left the river, homeward bound. Amongst them were hospital ships, clearly distinguishable by their broad green bands and conspicuous red crosses on both bows and quarters. A big action had taken place "somewhere in France", and the passing of the Red Cross vessels was the aftermath of a dearly-bought victory.
Yet nothing occurred to threaten the constant stream of shipping. It seemed reasonable to surmise that either the U-boat had met with an accident or else that she had transferred her energies to another area.
Meanwhile Ross and Vernon had been working hard, improving their seamanship. Under the instruction of the two sub-lieutenants they were making rapid progress in navigation; they could fix their position by the use of a sextant, were able to use the semaphore, and, generally, competent to carry out the duties required as midshipmen of the watch.
Captain Syllenger had long before overcome his prejudices against the sons of Flag Officers—at least in their case—and even expressed his willingness to grant them each a certificate of proficiency, should they wish to transfer to one of the cruisers of the Royal Navy.