On the Western Front... The Battle of the Bulge begins. German forces of Army Group B (Model), under the overall command of Field Marshal Rundstedt, launch an offensive in the Ardennes Forest, between Monschau and Trier, aimed at recapturing Antwerp and splitting the British and American armies. The attacking force consists of the 6th SS Panzer Army (Dietrich) on the right and 5th Panzer Army (Manteuffel) on the left. On the right and left flanks are the German 15th and 7th Armies. Allied forces are taken by surprise. The initial assault targets the line held by US 5th and 7th Corps, parts of US 1st Army (Hodges), in the US 21st Army Group (Bradley) as part of the Allied Expeditionary Force (Eisenhower). A brief artillery barrage precedes that attack. On the first day, German forces successfully breach the American lines. English speaking German troops, wearing captured uniforms and using Allied equipment, infiltrate behind the American lines causing some confusion and uncertainty in the rear areas. Poor weather prevents Allied ground attack aircraft from operating against the German armored columns. Meanwhile, US 3rd Army continues operations along the Saar River until news of the German offensive is received.

In Italy... Elements of British 5th Corps (part of British 8th Army) capture Faenza.

In the Philippines... Japanese planes attack American shipping while US aircraft strike at air bases (in continuing operations by TF38). On Mindoro, the landing forces consolidates the beachhead and begins construction of an landing strip.

In Liberated Greece... British General Scobie publishes the text of the Caserta agreement in which the communist guerrillas promised to work with the established government (in exile, at that time).