"The Poles mobilised in seven major groups shielding their hinterland from incursions that might come from any direction along a common frontier with Germany of almost indefensible length. Mobilisation was never completed in full: their only real defence against tanks could come from a handful of field mounted anti-tank guns that lacked sufficient mobility to deal with a foe who worked in mass and at speed. Concrete fortifications might help impose delay in a few places -- particularly in the more heavily defended sectors of the Danzig Corridor -- and rivers formed useful barriers behind which fresh mobile defences might assemble. The balance of power, if it were to be restored to Poland, could only be altered by super-human bravery."
--Panzer Division: the Mailed Fist, by Major K.J. Macksey, M.C.