Indeed till the invention of the petrol engine the Tank was doomed to be unpractical. Its three essentials--armour-plating, guns, and ability to surmount obstacles and traverse open country--demanded a large amount of this “free” power. Only, therefore, when an engine was produced whose proportion of power to weight was about 100 H.P. to every ten hundredweight, did the Tank become a possible and effective engine of war. Thus, till the time was ripe the Tank had been doomed to enjoy very brief excursions into the actual, and to sojourn, long forgotten, beyond the waters of Lethe. Does memory survive transmigration? Were General Swinton and his co-inventors aware of the Crimea Tank and the 1888 Tractor? In any case the matter is not one of great importance, for--to put it briefly--ultimately their Tank went, and the others did not. By October, 1914, Colonel Swinton and Captain Tulloch had independently worked out the details of an engine of war. Like the other early inventors, they imagined a machine that was to “arise” out of a cross between an armoured car and an agricultural tractor. It was to be slower, more formidable and far heavier than any armoured car that had yet been seen, a kind of “Land Cruiser” capable of plodding on its caterpillar feet across country right up to the enemy’s gun positions. Like the other early “mobile machine-gun destroyers,” it was to be strongly armed with guns and machine-guns, and so heavily steel-plated as to be impervious to shrapnel, H.-E. fragments and rifle bullets. It was to cross trenches with ease, and was to be capable either of cutting or of flattening the enemy’s wire in the mere act of its progress. By November Colonel Swinton and Captain Tulloch were in close touch with one another, and the child of their fancy descended from the clear regions of pure thought to battle its slow way forward amid the fogs and thornbrakes of actual experiment and official memoranda. Well-informed readers will perhaps wonder why the present authors have singled out Captain Tulloch and Colonel Swinton from amid “the press of knights.” Do they intend to lay the laurel on their brows? To declare that they alone invented the Tank? The chroniclers pretend to no such judicial powers. Be theirs rather the genial rôle of the Dodo in _Alice in Wonderland_, who at the end of the Caucus-race allotted one of Alice’s comfits to each of the competitors. As far, however, as they can disentangle the complexities of the evidence, it does appear to have been through these two enthusiasts that the Tank idea first took tangible shape. The notion was in the air, perhaps it took unsubstantial form in other minds before October, 1914,--it seems probable that it did in Mr. Diplock’s and Mr. McFee’s, for example. Perhaps, too, in other minds it was later to take clearer and more practical shape.