I had heard much of those spring tyres, so, taking advantage of the general rush for the pneumatically tyred Mercedes and the "rheumatically" tyred nondescripts, I lifted an oiled-paper curtain and plumped down on the woven paper cushion of old "_Ersatz_." As the other cars were quite filled up with the remainder of our party, the escorting German officer came in with me. "The imitation rubber," he began slowly and precisely, "makes many good things, but not the good motor tyres. It is resilient, but not elastic. It will stand the pushing but not the pulling. It is not strong, not tough, like the rubber from the tree. Ah, the English were very lucky always to have the real rubber. If that had been so with Germany--" Just to what extent a continuous supply of real rubber would have modified the situation for Germany I did not learn, for we started up just then, and the rest of the sentence was lost in the mighty whirl of sound in which we were engulfed. The best comparison I can make of the noise that car made--as heard from within--is to a sustained crescendo of a super-Jazz band, the cymbals of which were represented by the clankity-clank of the component parts of the steel tyres banging against each other and the pavement, and the drums of which were the rhythmic thud-thud of the _ersatz_ body on the lifeless springs. Although the other cars were rattling heavily on their own account, the ear-rending racket of the steel-tyres dominated the situation completely, and at the first turn I caught an impressionistic blend of blue and khaki uniforms as their occupants leaned out to see what was in pursuit of them. "It was unlike any sound I ever heard before," said one of them in describing it later. "It was positively Bolshevik!" All in all, I think "Bolshevik" is more fittingly descriptive than "Jazz-band-ic." It carries a suggestion of "savageness" quite lacking in the latter, and "savage" that raucous tornado of sound surely was. I could never allow myself to contemplate the primal chaos one of the American officers tried to conjure up by asking what it would be like to hear two motor convoys of steel-tyred trucks passing each other during a bombardment. The only sensible comment I heard on that question was from the officer who cut in with, "Please tell me how you'd know there _was_ a bombardment?"