In addition, a truck loaded with explosives and equipped with a time fuse should be kept ready by the entrance, so that it could be sent coasting down into the tunnel for some distance, there to explode automatically. Arrangements should be made for temporarily flooding the tunnel by means of culverts operated by sluice valves. ("If by chance the sluice valves should not act, Measure XVIII could be resorted to, or the tunnel could be blocked by one or more of the means ... mentioned in Measures VIII, IX, X, XI, and XII.") The tunnel should emerge inland, out of firing range from the sea. And it was imperative that it emerge under the guns and "in the immediate vicinity of a first-class fortress, in the modern acceptation of the term, a fortress which could only be reduced after a protracted siege both by land and sea." And so on. Even after drawing up all these elaborate precautions for closing the tunnel from the English end, the Channel Tunnel Defense Committee was left with some nagging doubts about their adequacy. In a concluding paragraph of its report, the committee pointed out that "it must always be borne in mind that, in dealing with physical agencies, an amount of uncertainty exists," and that it was "impossible to eliminate human fallibility." As a consequence, the members stated cautiously, "it would be presumptuous to place absolute reliance upon even the most comprehensive and complete arrangements." The committee also agreed, almost as an afterthought, that the Channel tunnel proposed by Sir Edward Watkin could not be sanctioned in the form envisaged, on the grounds that it did not meet the committee's conditions for emerging inland, out of firing range from the sea, and in the immediate vicinity of a first-class fortress. It also rejected, on the first of these grounds, a proposal by the lesser Channel Tunnel Company for a tunnel that would start from within Dover and for the sake of easy destructibility run right under a nearby corner of Dover Castle—and on the grounds that this entrance would be _too_ much in the vicinity of a fortress. And the committee objected that since the proposed entrance would emerge "in the heart of the main defences and in the midst of the town" any fire from these defenses "would inflict great injury on the town and its inhabitants, and the general defence would be much embarrassed."