The primary type of military formations used in the Battle of Antietam was Line formations.

Both Union and Confederate troops typically deployed in long, straight lines, which allowed for mass firing and maximized the effectiveness of their muskets and artillery. This formation was particularly advantageous in open fields, where visibility and the ability to deliver coordinated fire were crucial. However, line formations also made soldiers vulnerable to enemy fire, leading to high casualty rates. The battle showcased the strengths and weaknesses of this conventional tactic in the face of evolving military technology and strategies.