Oh, well in that case it is propaganda because there were no Tigers or panthers before then that could be used in a real offensive way. The Mk IV was classed as a heavy tank at the beginning of the war maybe that is what they are getting at?

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They shall grow not old as we that are left grow old Age shall not weary them, nor the years condemn
At the going down of the sun and in the morning
We shall remember them. Lest We Forget