Some armour Britain lost in dreadful gun battle (8)
I believe the answer is:
gauntlet
'some armour' is the definition.
(an armoured glove)
I don't understand how the remainder of the clue works.
(Other definitions for gauntlet that I've seen before include "that may be punishing for runner" , "Throw this glove down as a challenge" , "Indication of challenge" , "Handy thing to take up" , "It may be thrown down or run" .)