It's a curious mix of vehicles. The tanks are American M3 Stuart's masquerading as very early war German. The troops on horseback are supposed to be Polish troops, which ties in with the plain white crosses on the tanks, as those were the symbols used on German vehicles during the Polish invasion in 1939. This type of cross was gradually phased out after the invasions in the West - Holland, Belgium, France, Norway.
Why there is a Jeep in the picture is more difficult to explain as that type of vehicle didn't start being produced until 1941/42, long after the Blitzkreig period.
So, we're looking for a film dealing with the invasion of Poland and some kind of desperate cavalry charge by the Poles against German tanks.
Nick