American battle casualty in US hospital, in bed sick (6,4)

'american battle' is the definition.
(I know that Bunker Hill is a pitched battle)

'casualty in us hospital in bed sick' is the wordplay.
'casualty in us' becomes 'ER' (emergency room, US equivalent to casualty dept.).
'hospital' becomes 'h' (abbreviation for hospital on maps).
'in' means one lot of letters goes inside another.
'bed' becomes 'bunk' (bunk is a kind of bed).
'sick' becomes 'ill' (similar in meaning).
'er'+'h'='erh'
'bunk'+'ill'='bunkill'
'erh' put into 'bunkill' is 'BUNKER HILL'.