Just as the three-gun battery provided a serious obstacle to the passage of blockships round the Mole end, so also would it prevent the similar passage of other vessels endeavouring to secure alongside the berthing wharf on the inner side of the Mole preparatory to attacking the Mole batteries. Thus, if the Mole was to be stormed, _the storming parties must land on the outer side of the Mole_, remembering that the three-gun battery could not fire to the northward owing to being twenty feet below the top of the high outer wall. But the outer wall of the Mole was never intended for use as a berthing position for vessels, and probably never had been used by any vessel for such a purpose--hence the complete absence of all berthing facilities as described in an earlier chapter. The development of the argument concerning this projected attack had led us to the point where we needed to consider seriously the practicability of getting any vessel, or vessels, alongside the outer wall, of securing there, and of landing men thence for attacking the Mole batteries. The depth of water, the construction of the Mole, {74} the rate of the tidal current, and many other matters required careful examination. The depth was a doubtful matter; but, the operation being timed to take place near high tide so that the blockships could enter the canal, there was every likelihood of its being sufficient. Breakwaters when also intended as wharfs are usually built with their inner sides--i.e., the sides protected from bad weather--vertical like the face of an ordinary wall, but with their seaward sides formed of large blocks of material dropped more or less indiscriminately, one above the other, so that the wall will be jagged for the purpose of breaking up the waves in bad weather. In such cases a ship could not possibly secure to the seaward side without being severely damaged, and certainly could not remain there. At Zeebrugge, however, we had reason to believe that the seaward side of the Mole was nearly vertical and that no danger would accrue from jagged blocks of stone or concrete. [Illustration: SECTION of MOLE through No. 3 Shed]