1931 — , December 11

• CBI - China: Day 85 of 154 of the Japanese Invasion of Manchuria.

1936 — , December 11

• Spain: Day 148 of 985 of the Spanish Civil War.

1937 — , December 11

• Spain: Day 513 of 985 of the Spanish Civil War.
• CBI - China: Day 158 of 2,987 of the 2nd Sino-Japanese War.
  • Day 3 of 54 of the Battle of Nanking.

1938 — , December 11

• Spain: Day 878 of 985 of the Spanish Civil War.
• CBI - China: Day 523 of 2,987 of the 2nd Sino-Japanese War.
  • Day 61 of 81 of Japan's Operation GUANGDONG.

1939 — , December 11

• Finland: Day 12 of 105 of the Russo-Finnish War.
• CBI - China: Day 888 of 2,987 of the 2nd Sino-Japanese War.
  • Day 27 of 381 of the Battle of South Guangxi.

1940 — , December 11

• ETO - UK: Day 97 of 258 of the Blitz.
• MTO - North Africa: Day 3 of 63 of the UK's Operation COMPASS, their campaign in North Africa against the Italian troops in Egypt and Libya. In Egypt, British armored forces arrive in Sofafi to find that the Libyan and Italian divisions had already escaped. The infamous 4th Indian Division is reassigned to the Sudan, to be replaced by the 6th Australian Division.
• East Africa: Day 185 of 537 of Italy's East African campaign in the lands south of Egypt.
• CBI - China: Day 1,254 of 2,987 of the 2nd Sino-Japanese War.
• CBI - Thailand: Day 72 of 221 of the Franco-Thai War (Vichy France vs Thailand).

1941 — , December 11

• ETO: With war officially declared between both Japan and the United States, Germany and Italy both declare war on the United States.
  Spotlight...

  

  11 Dec 41 newspaper headline announcing that Germany
  and Italy have joined Japan in declaring war on the US

  Italian dictator Benito Mussolini made his declaration first, pledging the "powers of the pact of steel" were determined to win.

  Adolf Hitler then made his announcement saying he had tried to avoid direct conflict with the US but, under the Tripartite Agreement signed on 27 Sep 40, Germany was obliged to join with Italy to defend its ally Japan. "After victory has been achieved," he said, "Germany, Italy and Japan will continue in closest co-operation with a view to establishing a new and just order."

  Hitler accused President Roosevelt of waging a campaign against Germany since 1937 and blamed him for the outbreak of war in 1939.

  Technically, the United States never "declared war" on Japan, Italy or Germany in WWII. Rather, declarations were made in Congress that formally acknowledged the "state of war" that came into existence as each of the Axis powers made their formal declarations of war, authorizing and pledging the full resources of the US government and military to bring the conflict thrust upon the United States to a successful termination.
• Americas: US, Costa Rica, Cuba, the Dominican Republic and Nicaragua declare war on Germany and Italy.
• Germany: Mildred Gillars, aka Axis Sally, delivers her first propaganda broadcast to Allied troops (her last will be on 06 May 45).
• Russian Front - North: Day 95 of 872 of the Siege of Leningrad.
• Russian Front - Center: Day 71 of 98 of the Battle of Moscow.
• Russian Front - South: Day 43 of 248 of the Siege of Sevastopol, Crimean Peninsula.
• MTO - Libya: Day 246 of 256 of the Siege of Tobruk.
• CBI - Burma: Japanese troops invade Burma.
• CBI - China: Day 1,619 of 2,987 of the 2nd Sino-Japanese War.
  • Day 4 of 18 of the Battle of Hong Kong. The British garrison in Hong Kong begins to withdraw from the mainland to Hong Kong Island itself.
  • The US garrison in Peking is forced to surrender to the Japanese.
• CBI - Malaya: Day 4 of 55 of the Battle of British Malaya. The 11th Indian Division withdraws from Jitra toward Alor Star in northern Malaya.
• PTO - Marshall Islands: Day 4 of 17 of the Battle of Wake Island, aka the Alamo of the Pacific. Japanese troops attempt to land on Wake Island, but US Marine gunners and airmen repel the first landing attempt and sink two Japanese destroyers in the process.
• PTO - Philippines: Day 4 of 152 of the 1st Battle of the Philippines. Japanese troops make landings on the northern tip of Luzon and the island of Camiguin.

1942 — , December 11

• Russian Front - North: Day 460 of 872 of the Siege of Leningrad.
• Russian Front - North: Day 23 of 59 of the Battle of Velikiye Luki, near Leningrad. This stalemate does help ease the siege a little, but mostly it keeps German troops from being sent to other fronts.
• Russian Front - North: Day 221 of 658 of the Siege of the Kholm Pocket, USSR lays siege to the Kholm Pocket but the Germans hold out for a about a year and a half.
• Russian Front - Center: Day 18 of 21 of the Battle of Sychevka, Russia.
• Russian Front - Center: Day 17 of 26 of the 2nd Battle of Rzhev-Sychevka, Russia, launched by the Soviets as Operation MARS.
• Russian Front - Center: Day 17 of 22 of the Battle of Belyi, Russia.
• Russian Front - Center: Day 17 of 17 of the Battle of Luchesa (Vitebsk), Russia. The battle ends in a stalemate, but it has kept German troops from going to Stalingrad.
• Russian Front - Center: Day 17 of 29 of the Battle of Molodoi Tud River, Russia.
• Russian Front - South: Day 112 of 165 of the Battle of Stalingrad, bloodiest battle in human history.
• MTO - Algeria: During the past week, the Royal Navy lost the destroyers PENTLAN, PORCUPIN and BLEAN off Algeria.
• MTO - Tunisia: Day 25 of 178 of the Battle of Tunisia. US 12th Air Force provides Allied air support.
• MTO - Italy: US 9th Air Force B-24s bomb the harbor and surrounding areas at Naples.
• CBI - China: Day 1,984 of 2,987 of the 2nd Sino-Japanese War.
• PTO - Alaska: Day 188 of 435 of the Battle of Kiska, Aleutian Islands.
• PTO - Malaya: Day 296 of 357 of the Battle of Timor Island, a long guerrilla war ending in Japanese victory.
• PTO - New Guinea: Day 23 of 66 of the Battle of Buna-Gona.
• PTO - Solomon Islands: Day 127 of 187 of the Battle of Guadalcanal.

1943 — , December 11

• ETO - Germany: US 8th Air Force B-17s and B-24s bomb at Emden, killing 1,000 citizens and leaving another 12,000 homeless.
• ETO - Germany: Day 24 of 135 of the Battle of Berlin (RAF bombing campaign). Duisburg is attacked by 18 Mosquitos.
• Russian Front - North: Day 825 of 872 of the Siege of Leningrad.
• Russian Front - North: Day 586 of 658 of the Siege of the Kholm Pocket. USSR lays siege to the Kholm Pocket but the Germans hold out for a about a year and a half.
• Russian Front - South: Day 110 of 122 of the Battle of the Lower Dnieper River, USSR.
• MTO - Italy: RAF and US Air Forces provide air support for the Allied ground units.
• CBI - China: Day 2,349 of 2,987 of the 2nd Sino-Japanese War.
  • Day 40 of 49 of the Battle of West Changde.
• PTO - New Guinea: Day 84 of 219 of the Battle of Shaggy Ridge.
• PTO - New Guinea: Day 81 of 162 of the Battle of the Huon Peninsula.
• PTO - Solomon Islands: Day 41 of 295 of the Battle of the Bougainville Islands.

1944 — , December 11

• ETO - France: Day 133 of 284 of the Battle of Brittany.
• ETO - France: Day 88 of 236 of the Siege of Dunkirk.
• ETO - Germany: Day 84 of 145 of the Battle of Hürtgen Forest.
• ETO - Germany: US 8th Air Force sends 1,586 heavy bombers and 841 fighters to hit targets throughout western Germany.
• Russian Front - Finland: Day 88 of 223 of the Lapland War. Finland and Russia have joined forces to kick the Germans out of Finland's most northern province.
• Russian Front - Center: Day 58 of 206 of the Battle of the Courland Pocket in Latvia.
• Russian Front - Center: Day 51 of 99 of the Siege of Memel, a border town of Lithuania and East Prussia.
• Russian Front - South: Day 44 of 108 of the Battle of Budapest, Hungary.
• MTO - Austria: US 15th Air Force B-17s and B-24s attack targets at Moosbierbaum, Vienna, Matzleinsdorf, Kapfenberg, Tulln, Parndorf, and Graz.
• MTO - Italy: US and Royal Air Forces provides air support for the Allied ground units.
• CBI - Burma: Day 255 of 302 of the Chinese Salween Offensive.
• CBI - Burma: Day 28 of 31 of the Battle of Bhamo.
• CBI - China: Day 2,715 of 2,987 of the 2nd Sino-Japanese War.
  • Day 239 of 259 of Japan's Operation ICHI-GO.
• PTO - New Guinea: Day 350 of 597 of the Battle of New Britain.
• PTO - New Guinea: Day 234 of 481 of the Battle of Western New Guinea.
• PTO - Philippines: Day 53 of 299 of the 2nd Battle of the Philippines, aka the Liberation of the Philippines or the Philippines Campaign.
• PTO - Philippines: Day 53 of 73 of the Battle of Leyte.
• PTO - Philippines: Day 31 of 41 of the Naval Battle of Ormoc Bay.