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Jack / Jack Tar: Colloquial term for a sailor.
Jack Johnson: A German shell which explodes with black smoke.
Jacko: Colloquial term for a Turk.
Jacks: Derogatory slang for Military Police.
Jagdgeschwader : German fighter squadron.
Jagdstaffeln : German fighter flight.
Jäger : German rifleman.
Jäger zu Pferd : Mounted riflemen.
Jake: US/Canadian colloquialism for ‘good’.
Jakes: Latrines.
Jankers: Minor punishments.
Jannock: honest.
Japan: Bread.
Jasta: Shortened version of Jagdstaffeln.
Jemadar: Indian second lieutenant.
Jerry: Allied slang for German(s).
Jippo: A gravy or stew.
Jock: Scotsman.
Johnny / Johnny Turk: Slang for a Turk.
Jonathan: Colloquialism for Americans.
Juldee : ‘Hurry up’.
July Crisis (1914) : The time between Archduke Franz Ferdinand’s assassination and the outbreak of the First World War.
Jump / Jump Off: To commence an attack.
Jumping Off Point: The starting position for an attack.
Junkers CL-I: German reconnaissance biplane used in 1918.
Junkers D-I: German fighter plane, the first all metal aircraft of the war. Used in 1918.
Junkers J-I: German ground attack aircraft.
JUO: Jam of Uncertain Origin.