Begun in 1917 while Sir John Jellicoe was still First Sea Lord, the plan ultimately adopted--there had been several previous ones, dropped for military reasons--was devised by Vice-Admiral Roger Keyes, then head of the Plans Division at the Admiralty. From the first it was realized of course, by all concerned that the element of surprise would be the determining factor; and it was therefore decided that the attempt to block the harbours should take place at night. It was also clear that, under modern conditions of star-shells and searchlights, an extensive use would have to be made of the recent art of throwing out smoke-screens; and fortunately, in Commander Brock, Admiral Keyes had at his disposal just the man to supply this need. A Wing-Commander in the Royal Naval Air Service, in private life Commander Brock was a partner in a well-known firm of fire-work makers; and his inventive ability had already been fruitful in more than one direction. A first-rate pilot and excellent shot, Commander Brock was a typical English sportsman; and his subsequent death during the operations, for whose success he had been so largely responsible, was a loss of the gravest description both to the navy and the empire. {227} The next consideration was the choosing of the block-ships, and for these the following vessels were at last selected--the _Sirius_ and _Brilliant_ to be sunk at Ostend, and the _Thetis_, _Iphigenia_, and _Intrepid_ to seal the canal entrance at Zeebrugge. These were all old cruisers, and they were to be filled with cement, which when submerged would turn into concrete, fuses being so placed that they could be sunk by explosion as soon as they had reached the desired position; and it was arranged that motor-launches should accompany them in order to rescue their crews. Unfortunately Lieutenant Ivan B. Franks, who was responsible for the block-ships, was laid aside, the day before the event, by an attack of appendicitis, and, at his urgent request, his duties were undertaken by his friend, Lieutenant Billyard-Leake--a very able young officer, then barely twenty-two years of age.