[jivemi]

Actually you've already got what you need. The 75mm guns in the trees north of the river can x-fire smoke before anybody moves, screening the advance. (They're not too accurate, but hey, whaddaya expect for 1939?) Any enemy LOS that remains can be smoked off by infantry until the armor shows up.

Additional arty assets can be assigned to identified or likely occupied defensive positions while your guys move up. If you planned it right--and you're a little lucky--your smaller squads can survive whacks from even dug-in half-platoon size Polish units if they're already pinned by bombardment (or "area" shooting [z-fire]). Then bring up armor to assist.

It's scenarios like this that reflect the essence of combined arms tactics. Co-ordination is the key, along with smoke in the first stages of assault.