Noun
line of battle
The area in which one concentrates one's resources on a struggle
Source: en.wiktionary.orgThe battleline between good and evil runs through the heart of every man. Aleksandr Solzhenitsyn
Lion lost speed, causing her to fall behind the rest of the battleline, and Beatty was unable to effectively command his ships for the remainder of the engagement. Source: Internet
The Gary Cooper movie They Came to Cordura contains a scene of a cavalry regiment deploying from march to battleline formation. Source: Internet