Term | Explanation |
| Bagration | Operational codename for Soviet strategic offensive against the German Army Group Centre, June 1944. |
| Barbarossa | Operational code name for the German invasion of the Soviet Union in June 1941. (Barbarossa, or Red Beard was the nickname for Emperor Frederick I, who attempted to unify Germanic states in the 12th century.) |
| Battleaxe | Operational code name for the British offensive in North Africa intended to relieve Torbuk, June 1941. |
| Baytown | Operational code name for the Allied landings in southern Italy, September 1943. |
| BCRA | Bureau Centrale de Renseignements et d'Action - de Gaulle's secret intelligence service. |
| BEF | British Expeditionary Force. |
| Bernhard | Operational code name for German scheme to counterfeit British bank notes and put them into circulation - began in 1942. |
| Bestrafung | Operational code name for German punishment air attacks on Belgrade, April 1941. |
| Blitzkrieg | Lightning War - a term used to describe the rapid German invasions using fast, piercing armoured formations. |
| Bodenplatte | Base Plate - Operational code name for the German air offensive against Allied airfields in north-western Europe, January 1945. |
| Bolero | Operational code name for the build up of US forces in Britain prior to the invasion of France. |
| Bomb, The | Slang term for the computers used at Bletchley Park, England, to decode German Enigma messages. |
| Brevity | Operational code name for the British offensive in the Halfaya Pass, May 1941. |
| Brimstone | Operational code name for the proposed Allied invasion of Sardinia, 1944. |
| Bulge, Battle of the | Term used to describe the actions following the German offensive through the Ardennes forests in December 1944. |
| Buzz Bomb | Nickname for the German V-1 flying bomb. |