The Tommies of the Great War used and developed a unique slang of their own. It was created mostly from Indian and Arabic dialect words picked up and passed on from the previous campaigns in India and Egypt, coupled with the Tommies' rather awkward pronunciation of some of the more common French words and phrases.
Some of the expressions rapidly fell out of popular use once the war ended. However, some persisted and are still with us in the modern language of today.
Many of the phrases use words from the phonetic alphabet, or Signalese as it was colloquially known.