The use of artificial fog in war was by no means an entirely new idea. The device had already been utilised by our naval forces off the Belgian coast, and a quantity of data on the subject was available as a result of its use in fighting on land. But all forms of fog screens--and there were many--had hitherto possessed disadvantages which would militate against satisfactory results in an enterprise such as we contemplated. The main difficulty attached to the smoke apparatus at Dover was that a very visible flame was emitted; this would have completely given our presence away as the smoke was intended to _hide our presence_ and cover our advance. Some attempts had been made to surmount this difficulty, but experiments proved the apparatus to be hopelessly unsuited to our requirements. The reader, however, will not desire to be introduced to a highly technical treatise on this subject. Suffice it to say that, as a result of prolonged experimental work, a new type of fog was evolved which satisfied all requirements. The trials were not altogether devoid of humour. It is rumoured that on one occasion a fog produced in the Dover {100} Straits refused to dissipate itself for three days, with the result that mercantile captains said some very hard things about the clerk of the weather. The blockships and _Vindictive_ were fitted out at Chatham. That dockyard was already being taxed to its utmost. The situation demanded that every man should strive to exceed his previous utmost efforts--one of the few points on which our enemies may congratulate themselves. Secrecy was, of course, essential. Yet in the case of the ships fitting out at Chatham the number of men who played an indirect part in the operation ran into four figures. The same thing applied at Portsmouth where the _Iris_, the _Daffodil_, and the submarines destined to attack the railway viaduct at Zeebrugge were fitted out. The director of Naval Construction, Sir Tennyson D'Eyncourt, and the Director of Dockyards, Rear-Admiral L. E. Power, brought all their valuable knowledge, and that of their respective staffs, to bear on the problem. Much of the usual formality governing inter-departmental procedure was waived. Paper work was reduced to a minimum. The real nature of the operation was made known to few at that period. The war had taught men not to ask questions unless the information was an absolute necessity. Nevertheless many must have wondered what was afoot; special steps had to be taken, therefore, to prevent leakage of information, of which more anon. {101} CHAPTER VIII THE PERSONNEL. SECRECY. TRAINING. SOME PERSONALITIES.