Conversation so far:
What did the Kray twins have to do with the National Service in the British Army?
The Krays were called up to do National Service in the British Army in March 1952
What did the Kray twins do at the depot of the Royal Fusillers?
Although the Kray twins reported to the depot of the Royal Fusiliers at the Tower of London, they attempted to leave after only a few minutes.
Why did the Kray twins attempt to leave the depot of the Royal Fusillers?
Were the Kray twins forced to stay in the army?
The corporal that tried to stop the Kray twins from leaving the Royal Fussilers got punched by Ronnie. The police arrested them and were turned over to the army.
Where the Kray twins charegd for punching the corporal at the Royal Fussillers?
The Kray twins were transferred to Shepton Mallet military prison in Somerset for a month to await court-martial.
What did the British army to with the Kray twins?
The Kray twins were dishonourably discharged from the army. They were eventually transferred to a civilian prison.

Question: how long were they in the prison in somerset?
Self-contained rewrite: How long were the Kray twins in the prison in Somerset?