They did, sort of, starting in the 1940s. The tank make/model were replaced by arbitrary codes, but it was done sloppily and many of the tanks could be re-ident

They did, sort of, starting in the 1940s. The tank make/model were replaced by arbitrary codes, but it was done sloppily and many of the tanks could be re-identified. (See page 80 of the paper @dooglius posted above). Still, the idea that this could leak valuable information is probably more obvious in hindsight, and sequential serial numbers do have some upsides. If there's a design flaw in one version of the gearboxes, you can just pull everything with a serial number between XXXX and YYYY. With randomized numbers, you'd have to maintain some master database, which is a lot harder when most of logging is done with pen-and-ink ledgers, carbon copies, and maybe punchcards.