For 1911–12 boats a similar principle was followed, and there was also still further acceleration. These latest boats are somewhat faster than heretofore, and an interesting innovation in the case of one of them--the Thornycroft type--is the appearance of the Diesel engine for partial propulsion instead of steam. As a matter of fact, this idea did not eventually materialise, owing to various circumstances of the side issue nature. More or less contemporaneously with this the Yarrow firm in the _Archer_ and _Attack_, their special destroyers, evolved a system of super-heated steam, which led to a very considerable increase in speed, as compared with older methods. A conflict between steam and “gas engines” for destroyers was, therefore, in 1912, a probable feature of the early future, a conflict still in the “to-morrow” stage; but it may be unwise to place too much reliance on the fact that a similar conflict with motor cars ended in the practical extinction of steam, for all that the probabilities point in that direction. The superior convenience of the Diesel engine whether for destroyers or larger ships is obvious, but there are undoubtedly still certain practical difficulties which cannot be ignored. In 1912 the destroyer may be said to have reached its apotheosis. Later boats are considerably larger, more powerfully armed, and occasionally a trifle faster, but, taken all in all, they do not indicate any definite advance on the “general idea” of a destroyer. Novelty, such as it exists, is confined to the introduction of flotilla leaders. The idea is not new, since the Germans hit on it for torpedo boats long before destroyers as we understand them were evolved. There is also the still older idea of our original _Swift_. The integral notion is in each case the same. The idea is to provide the commander of the flotilla with a boat swifter and more powerful than those of his normal command, and thus to enable him to reinforce as requisite any particular portion of his squadron. Thus viewed, the idea is, of course, as old as naval warfare itself, or, for that matter, any warfare whatever; and it is strange that the principle of the superior power of the chief should ever have been allowed to lapse. It is, however, curious to note that at the outbreak of the present war the British was the only Navy in which the idea was in actual practice. Not till the war is over shall we learn whether the seeming advantage is or is not of real value. All the indications, however, are that it should be an immense asset if properly handled. _GUNS OF THE WATTS ERA._ The principal guns of the Watts era are as follows:--