The TA's Medical Corps is taking over Astley Park in Chorley. The area will reverberate to the sound of enemy gunfire as its members evacuate a 'casualty' from a battlefield scene and provide emergency care in a field medical tent.
The Medical Corps hopes the demonstrations and information stands will encourage new members to sign up.
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He served in Margaret Thatcher's Cabinet as Home Secretary in 1989 and was also a former Governor of Bermuda.