A martial archetype for the Fighter class in 5e
The archetypal Commander is an inspiring leader, trained to coordinate the efforts of a fighting force making them a more effective battle unit.
To use the Commander martial archetype, simply add it as an additional Martial Archetype option to the Fighter class.
Starting at 3rd level, you select naturally defensible positions for making camp. While taking a long rest you and any creatures you choose within your camp perimeter have at least half-cover (unless the terrain does not accommodate it at the DM's discretion), and cannot be surprised by any attackers that approach from outside your camp perimeter.
At 3rd level you gain the ability to inspire others with your example. When you land a critical hit or reduce a creature to 0 hit points with an attack, you may use your reaction to boost the morale of all chosen creatures within 60 feet (but not yourself). Each chosen creature removes the frightened effect and gains advantage on their next attack roll, saving throw, or ability check; this advantage is lost if unused within one minute.
Starting at 5th level, after you roll for initiative you may choose to give your initiative result to a willing creature within 30 feet that can hear and understand you. That creature's initiative becomes the result you gave them. Your initiative result becomes 1.
At 10th level you may choose up to two creatures to give your initiative result to, and you break the tie in any order you decide. At 15th level you may choose up to three creatures, and at 18th level you may choose up to four creatures.
Starting at 7th level, as an action you may coordinate a defensive formation. You must choose at least two non-hostile creatures (including yourself) within 15 feet of you to use this ability.
You and each chosen creatures adopt a defensive formation and do not provoke opportunity attacks unless taking the Dash action. If at least half of all creatures in the formation are bearing shields then the formation also has half-cover.
This effect ends for a creature when it moves more than 15 feet away from you, and it ends for you when none of the chosen creatures are within 15 feet of you. Once you use this ability, you can't use it again until you finish a short or long rest.
At 10th level you learn to lead the charge effectively. To use this ability you move at least 20 feet in a straight line before making a melee attack in the same turn. Each of your attacks this turn deal an additional 1d6 damage. All creatures you choose that were within 30 feet of your starting position gain the same benefit until the beginning of your next turn: the creature must move at least 20 feet in a straight line before making a melee attack to gain an additional 1d6 damage per attack during their turn. Once you use this ability, you can't use it again until you finish a short or long rest.
Starting at 15th level, you may spend an action to rally demoralized, beaten, and routed allies. All creatures you choose within 30 feet (but not yourself) remove the frightened and stunned effects. Each creature may also spend any number of hit dice to restore hit points as if it were a short rest. Once you use this ability, you can't use it again until you finish a short or long rest.
At 18th level you learn to concentrate the efforts of a fighting unit on a single target. As an action you choose a target within sight. All creatures (other than you) within 120 feet that can hear or see you may use their reaction to make one attack against the chosen target if they are in range and are already holding the appropriate weapon. Once you use this ability, you can't use it again until you finish a short or long rest.