My university German professor claimed (in 1989) that the original full name in German for a tank (of the armored vehicle sort) had been
This seems possible, but unlikely. Web searches suggest that it is probably not legitimate, but I have not found anything conclusive.
In this old Wikipedia Reference Desk discussion someone claims to have seen it in print, but provides no citation or provenance. I remain doubtful. Other web pages suggest –kampfwagen; the name panzerkampfwagen does seem to be attested, but what about the longer form? (And my professor said kraft, not kampf.) Schützengraben itself is of course well-attested. Google Book Search finds only one example, not actually a book, but a web forum discussion (in German) of extremely long words.
Was either of these very long words ever (with kraft or kampf) used seriously? Or is this, like similarly-long words in English, used mainly as a facetious example of an absurdly long word? If the latter, is it actually known in German, or is it used principally by English speakers as a facetious example of an absurdly-long German compound word?