Lloyd - Passchendaele: the lost victory of World War I

5.9: 15cm German field howitzer

Army: Collection of corps (usually between two and seven) commanded by a General

Army Group: Collection of armies (usually consisting of two or three)

Battalion: Unit of infantry (nominally up to 1,000 strong) commanded by a Lieutenant-Colonel

Battery: Organization of artillery pieces (usually containing between four and six guns)

Bite and hold: Operational method that prioritized limited attacks against local points of tactical importance aimed at provoking wasteful counter-attacks

Boche or Bosche: Slang term for Germans

Brigade: Major tactical formation commanded by a Brigadier-General. Three brigades made up a British division (each brigade containing four battalions). French and German brigades operated on a different system, each with two regiments

Corduroy road: Makeshift wooden road covered with sand, often used in swampy conditions

Corps: Group of divisions (usually between two and five) commanded by a Lieutenant-General

Creeping barrage: Moving wall of shellfire that swept across the battlefield at a predetermined pace. Designed to keep defenders heads down and escort infantry on to their objectives

Digger: Term for Australian troops

Division: Basic tactical unit on the battlefield employing between 10,000 and 15,000 men, with supporting medical, engineering and artillery arms, commanded by a Major-General. By 1917 most divisions were not up to this strength, with many German divisions containing only around 8,000 infantry

Eingreif Division: Literally intervention division. Specially trained reserve unit kept out of range of enemy artillery and brought forward to seal off enemy penetrations and counter-attack whenever possible. A key element of German defensive tactics in 1917

Flanders Lines (Flandern Stellungen): A series of three heavily defended Flanders Lines ran from Lille to the Belgian coast

Group: German corps assigned to a permanent sector of the front

Hindenburg Line: Major German defensive system constructed during 191617

Jagdgeschwader: German Air Service fighter wing (containing four Jagdstaffel)

Jagdstaffel (Jasta): German Air Service fighter squadron (usually containing between nine and twelve aircraft)

Jger: Elite German light infantry

Landsturm: German militia units comprising inferior troops used for local defence

Lewis gun: American-designed light machine-gun first introduced in 1915 and widely used in the BEF

Materialschlacht: Literally material battle. German term for the kind of industrialized, mass warfare that emerged on the Western Front in 1916

Minenwerfer: German heavy trench mortar

Pillbox: Reinforced concrete blockhouse

Poilus: Literally hairy ones. Slang for French soldiers

Regiment: Organization of infantry battalions. French and German divisions contained four regiments (each of three battalions). The British regimental system differed from continental use and regarded the regiment as a permanent organizational unit for its battalions

Zero Hour: Time at which an attack would commence