'According to General Eric von Manstein, the Donbas had a special significance in Hitler's mind: the Donbas had "played a fundamental part in Hitler's operational calculations as far back as 1941, for he considered possession of it to be of vital importance to the outcome of the war." The Germans "extracted substantial quantities of Donetz (Donbas) coal for our own [i.e., German] use," but "all the bunker coal for the railway supplying this vast territory had to be brought out from Germany because Donetz coal did not suit our [German] locomotives." The fighting capability of the Soviet forces even long after much of the Donbas was lost failed to dissuade Hitler from his belief in the absolute importance of the Donbas to the German war effort.' - 'Freedom and Terror in the Donbas: A Ukrainian-Russian Borderland, 1870s-1990s' by Hiroaki Kuromiya, pp.262-3 ( https://books.google.co.uk/books?redir_esc=y&id=d5b689wW7qwC&q=resources#v=snippet&q=hitler&f=false )