AERIAL PHOTOGRAPH OF THE CANAL ENTRANCE.
Taken shortly before the enterprise, showing the sandbanks narrowing the entrance channel. At the top of the photograph a dredger at work indicates the position of the approach channel
Now let us imagine for a few moments a duel between this battery and a warship within—say—one thousand yards. The reader probably knows that such a distance nowadays comes within the definition of "point-blank range"; i.e., a range at which a gun practically cannot miss a ship. Picture, then, an average-sized vessel of three hundred feet in length. The guns could hardly miss her—in fact, the gunners could select which particular portion of her should serve as their target. The ship's guns would return the fire. The most vulnerable portions of the battery ashore are the guns themselves. The muzzle of each gun showing just above the wall would, as viewed from the ship, cover barely one square foot in size. Now at golf we call it a "fluke" when a golfer holes out from the tee although he has attained his object. (I apologise for this to non-golfers.) Similarly, if the ship's gun hits the shore gun we should call it a "fluke," although that is the object forming the target. And, as already implied, if the shore gun misses the ship, that also will be a "fluke." On the face of it, it certainly does not look as if the ship would stand much chance, even at a distance of one thousand yards. But how if she is closer? If a thousand yards is point-blank range, how shall we designate a hundred yards?
At the eastern end of the broad part of the Mole, and on its floor level, the Germans had erected a battery of three heavy guns. These were so placed that they could fire on any incoming vessel immediately she rounded the lighthouse. Woe betide a vessel attempting to do so in the face of such guns. The latter were probably of the 5.9-inch type. Under water, immediately below this battery, we eventually found some submerged torpedo tubes, but I am not aware as to whether they were constructed before the blocking operation or not; their direction of fire was similar to that of the guns above them.
Close westward of these batteries of heavy guns and torpedoes, and standing against the high outer wall, the Germans had constructed a long shed of reënforced concrete; this shed provided the living space for the personnel of the Mole garrison.
The total numbers of Germans on the Mole probably reached not less than a thousand. Although this number may include the personnel of the seaplane base yet they would all be available for the defence of the Mole in case of an attack.
Slightly to the westward of the garrison's quarters, trenches had been sunk in the floor of the Mole and surrounded by three complete sets of barbed wire entanglements. It was believed that the usual accessories of a coast fort—e.g., searchlights and range-finders, etc.—were placed on the outer wall parapet, and that there would probably be some small guns there also.
The Booms and Torpedo Craft
So much for the Mole itself. Across the channel the Germans had placed booms. One of these, consisting of four Rhine barges, was moored between the eastern end of the broad part of the Mole and a buoy situated two hundred and seventy yards to the southward. These barges were filled with stone, had nets slung beneath them, and were connected together by wire hawsers. If a surface vessel attempted to pass between the buoy and the Mole she would be brought up by this boom and probably damaged by collision with one of the barges. If a submarine attempted to dive underneath the barges she would be caught up in the nets. The other boom consisted of entanglement nets moored between a series of buoys to the southeastward of the barges. Any ship attempting to pass through them would probably have her propellers entangled, with the result that her engines would be brought to a complete stop. Thus, whichever boom was encountered by a ship, the latter would, at the least, be partially disabled and stopped. The Mole batteries could then have sunk her at their leisure by gunfire. The only route by which a vessel could pass clear of these two booms was that between the southeastern barge and the northern entanglement net; i.e., within two hundred and fifty yards of the heavy gun battery on the Mole. But even if, by dint of good fortune or special good management, a vessel managed to pass the Mole batteries and the booms, she would still have to run the gantlet of the naval vessels in the anchorage and the batteries on shore before reaching the canal.