Inconclusive Baltic coast 4–10 September Northern Front Southern Front Battle of Lasy Królewskie (Polish: Bitwa w Lasach Królewskich, Battle of Royal Forests) refers to the battle on 1 September 1939 near Janowo and Krzynowłoga Mała during the Battle of the Border of the Invasion of Poland.

The German Third Army attacked towards Warsaw from East Prussia, but became entangled by the Mlawa fortifications.

The Wodrig Corps could not flank the Polish position due to the swampy ground.

Along the Ulatkowka river, Polish Uhlan cavalry (elements of 11th Cavalry "Legions'" Regiment) stopped attacks by the German 1st Cavalry Brigade.

However, the Poles did stall the German Third Army advance.