A protracted battle is a long and drawn-out conflict, usually involving a SIEGE. In this case, the crossword solution for the term 'protracted battle' is 'SIEGE'. A SIEGE is a military tactic in which an attacking force surrounds a defended location in order to cut off supplies and communication, with the goal of forcing the defenders to surrender. Historically, sieges have been used to great effect, such as during the Hundred Years' War between England and France, where the English used sieges to capture French castles and towns.