Through tough training, the soldiers built deep comradeship with each other.

comradeship 是由名词 comrade（同志、战友）加上后缀 -ship 构成的名词。后缀 -ship 表示"状态、关系、身份"，所以 comradeship 指的是"同志情谊、战友情谊"这种亲密关系。