That portion of the outer wall which formed the lighthouse extension of the Mole was broadened, above the sea level, to about seventeen feet throughout its length. The pathway was similar to that just described, but fifteen feet in width. This portion of {28} the Mole was hollow, a tunnel inside it running from the third portion of the Mole to the base of the lighthouse. The navigable channel from the open sea to the canal entrance could only be maintained in an efficient state by means of continual dredging, owing to the silt. The channel passed close to the lighthouse at the end of the Mole, and then in a fairly direct line, for a distance of three-quarters of a mile, to a position midway between the extremities of the two piers marking the canal entrance. Thence the deep water channel passed slightly to the westward of the central line between the piers. This latter portion of the channel had become exceedingly narrow by virtue of the sandbanks which had formed on either side of it and which actually uncovered at low water. A vessel drawing more than twelve feet or so was forced to keep exactly in the middle of this dredged channel to avoid grounding. Photographs taken at or near high tide gave the channel the appearance of extending from one pier to the other, at least a distance of one hundred yards; those taken near low water showed how narrow the channel really was. In the region of the two piers the silting of the sand was more rapid than elsewhere: the narrowest part of the channel was situated near the shore ends of these piers. [Sidenote: Defences on the Mole] The Germans had not rested satisfied with either the Mole, the canal entrance, or the lock as they found them. The Mole itself had been transformed into a fortress, and further defences had been constructed for the purpose of guarding the canal. [Illustration: A PORTION OF THE GERMAN BATTERY ON THE LIGHTHOUSE EXTENSION OF THE MOLE. VIEW OF THE CANAL ENTRANCE WITH ITS CURVED PIERS. This photograph was taken at high tide. Note the Mole in the distance] Batteries were placed on both sides of the canal entrance. These ranged from four-inch guns to {29} twelve-inch guns. Barbed wire entanglements were erected along the shore line; trenches, containing machine guns, were dug close behind them. It was believed that a boom of some sort, capable of being hauled across the channel or removed at will, was kept handy to the outer lock gate. The gate itself, "caisson" is the correct technical term, was withdrawn into an armoured housing, impervious to shells or bombs, when the lock was opened to allow vessels to pass through. The caisson was also provided with an armoured roof for defence against aerial bombs. The lights on the wooden piers were only lit when specially required to guide a German vessel to the entrance.