During the Battle of Antietam, soldiers primarily communicated using messengers and signal flags.

With no modern technology like radios or telephones, commanders relied on mounted couriers to deliver messages swiftly across the battlefield. Signal corps units also utilized visual signaling with flags to convey orders and relay information between units stationed at various points. This method of communication was vital for coordinating movements and responses in the heat of battle, despite the challenges posed by the chaos and noise of combat, which often hampered effective communication.