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FA: Field Artillery, Field Ambulance or slang for 'nothing'.
Fahnenjunker: German officer cadet.
Fahnrich: German ensign.
faire suisse: 'to do Swiss', to have money but not spend it on a meal/drink for comrades.
Fairey Campania: British naval reconnaissance biplane often used with floats on aircraft carriers.
FANY / Fanny: First Aid Nursing Yeomanry Corps, female recruits who worked in medical support.
Farman F-40: French two-seater armed reconnaissance/light bombing biplane, mainly used between late 1915 and 1917.
Farman F-50: French bomber biplane used during 1918.
Farman HF-20: French designed biplane used for reconnaissance and light bombing.
Farman MF-7: French reconnaissance biplane, used in 1914 and 1915.
Farman MF-11: French reconnaissance/light bombing plane.
Fascine: Bundles of wood – usually sticks/brushwood – used to fill in trenches and ditches. In WW1, they were used to allow tanks to cross trenches.
Fatherland Party: German political pressure group on the right wing.
Faustschlag : German offensive of 1918.
FB: Fighting Biplane.
FE-8: British fighter plane.
Felixstowe F-Types: Series of British flying boats.
FD: Field Dressing.
Fea: Flieger-Ersatz-Abteilungen: German air training squadron.
Feldfebel: Russian/Bulgarian senior sergeant.
Feldgrau: Field Grey, the colour of the German uniform. Also used to refer to German soldiers.
Feldwebel: German company sergeant major.
Fernleaf: Someone from New Zealand, derived from the New Zealand Expeditionary Force's cap badge.
Feu pilote: French signal light.
Fewewa: Feldwetterwarte. The German Army HQ's weather station.
FFD: First field dressing.
FF: Frontier Force, Indian Army.
Fiat Revelli-Gun: Italian machinegun used throughout the war.
fiche blanche : White Ticket, a French casualty designation for those who couldn't be moved.
fiche rouge : Red Ticket, a French casualty designation for those who could be moved.
Field Dressing: Kit carried by soldiers to treat wounds, smaller than the 'shell dressing'.
Field Postcard: A postcard with a series of pre-printed messages which the soldiers deleted to leave his chosen one. Did not require censoring and travelled quicker.
Field Punishment Number 1: A method of discipline which involved being tied to a wheel or staked out and put on a bread and water diet.
Fighter Plane: Aircraft designed for attacking other planes.
Fill: The requirements of a tank to make it battle ready, including petrol, oil, ammunition etc.
Fire-bay: A length of trench manned ready for an enemy attack.
Fire-step: A trench was normally deep enough for soldiers to walk along completely concealed. The fire step ran along the forward wall and allowed soldiers to peer or fire over the top.
Fire-trench: Front-line trench.
First reinforcement: The first reinforcements a unit received came from it's 'cadre', a body of men held back from the initial attack, the 'first reinforcements'.
Five-nine: A German 5.9inch shell.
Fixe! : Look forward.
FJ: Feldjäger, Austro-Hungarian rifle corps.
FK: Feld-Kanone: German field gun.
Flak: Anti-aircraft fire.
Flakgruko: Flakgruppe-Kommandeur, corps commander of German anti-aircraft units.
Flamga: Flugabwehr-Maschinengewehr-Abreilungen, German Anti-Aircraft machine gun detachments.
Flaming Onion: German anti-aircraft shell.
Flank barrage: A barrage aimed at one flank.
Fleabag: Sleeping bag.
Flechette: Darts dropped from planes targeting people.
Fleet in Being: A military/political strategy of intimidating an enemy with the possibility your fleet might attack.
Fliegende Divisionen: Independent German divisions.
Flight: RAF unit of 5-6 planes.
Fly Boys: Men to fled to Ireland to avoid conscription.
Flying Circus: Allied nickname for the German Army Air Service Jagdgeschwader (Fighter Group) formed in 1917 by elite pilots and led by the Red Baron.
Flying Pig: Mortar bomb.
FMO: Full Marching Order.
Fokker D-I to D-IV: Series of German fighter biplanes used from 1915 to 1916.
Fokker D-VI: German fighter biplane which saw limited action in 1918.
Fokker D-VII: German fighter biplane of 1918.
Fokker D-VIII: German fighter monoplane used in late 1918.
Fokker Dr-1: German triplane fighter craft introduced in 1917, temporarily withdrawn due to faults in late 1917, reintroduced and withdrawn as obsolete in 1918.
Fokker E-Type: German monoplane introduced in 1915, considered to be the world's first dedicated fighter plane.
FOO: Forward Observation Officer, an artillery spotter.
Forby: Cleaning cloth.
Fougasse: Form of mine.
Four by Two: Small cloth used to clean a rifle, named after it's size.
Four Minute Men: American public speakers spreading official propaganda, they were named after the length of their speeches.
Fourragère : French mark of distinction worn on the shoulder.
Fourrier: French quartermaster sergeant/corporal.
Four two: German 4.2 inch shell.
Fourteen Points: US President Woodrow Wilson's programme for peace.
FP: Field Punishment.
Franc-tireur: Partisan or 'irregular' soldier, shot on sight by Germany.
Franco-Russian Alliance: An series of agreements in 1894 whereby France and Russia agreed to assist each other in the event of a German attack. Inflamed German fears of encirclement.
Fray Bentos: Slang for corned beef.
Fregattenkapitän : German naval rank.
Freikorps: Private military units funded by industrialists and formed from ex-soldiers in late 1918 to stop a feared left-wing revolution.
Friedrichshafen FF-33: German two seater reconnaissance floatplane.
Friedrichshafen FF-49: Armed German two seater reconnaissance floatplane.
Friedrichshafen G-Types: Series of German bomber biplanes introduced in 1916.
Fritz: Nickname for all Germans.
Front: General areas of military operations.
Fruntas: Romanian Private 1st Class.
FSMO: Field Service Marching Order, the infantryman's full load of equipment.
Fukla: Funker-Kleinabteilung, German divisional wireless detachment.
Funk hole: A dugout.
Funky Villas: Fonquevillers