Finland. Soviet assaults on the Mannerheim Line around the village of Summa gain no ground with further heavy losses. North of Lake Lagoda, the line at Kollaa holds and Finnish IV Corps pushes Soviet 75th and 139th divisions back to Ägläjärvi. In the far North, 3 Finnish companies under Captain Pennanen (retreating since Nov 30) hold Soviet 52nd division at Höyhenjärvi where they will stay frozen for two months.
Battle of Heligoland Bight. 22 RAF Wellingtons (9, 37, 149 Squadrons) are sent in daylight to bomb ships off the German North Sea coast (site of the famous WWI naval battle). They reach their target safely but find only ships in harbor which they do not bomb find to avoid German civilian casualties. Returning home, they are attacked by about 50 Messerschmitt fighters. 10 bombers are shot down, 2 ditch flying home and 3 crash land. 2 Messerschmitts are also shot down. RAF suspends daytime bombing until April 1940.