Considered in a general manner, there were three lines of enquiry from which a solution of the problem might be forthcoming. Firstly, that concerning the destruction of the guns or their crews, or both, or diverting their fire, by means of action from a distance. Secondly, that of attaining a similar result by action on the spot. Thirdly, that of rendering the blockships invisible during their passage. These may be dealt with briefly. The first method entailed the use of either gun-fire or poison gas. The outcome of a gun-fire duel between a ship and a battery has already been described sufficiently to show that the chances of destroying the battery guns are exceedingly small. The use of poison gas has been shown to be inadvisable. The third method--that of rendering the blockships invisible to the battery--would have entailed the use of a smoke screen. If such a screen could have the effect mentioned it is obvious to the meanest intellect that it would also have the effect of hiding their destination from the blockships just at the critical period when it would be absolutely essential to see exactly where they were going. [Illustration: A PORTION OF THE BROAD PART OF THE MOLE. Note the concrete submarine shelter (white)] And so no method would suffice, except the second mentioned above, namely, destroying the guns or their crews, or both, or diverting their fire, by means of action _on the spot_. This entailed an attack on the Mole itself, carried out by vessels actually berthed {73} alongside. The author, although well aware of the unpardonable fault of repetition, desires at this stage to lay great emphasis on the fact that an attack on the Mole itself could only be designed as a diversionary measure calculated to directly assist the blockships past one of the positions of danger. The reader is requested to pardon anticipation. Subsequent to the operation, many of the public appeared to have formed the idea that the attack on the Mole was the main attack, and that the use of the blockships was a sort of afterthought. I shall have more to say about this later.