I was kicking around the idea of 3 promotion lines for a melee unit (not anti-calvary). All the numbers and perks are just tossed out ideas:
With the first promotion, choose one of three paths:
(1) Combat;
(2) Marine; or
(3) Special Forces
Combat 1 = +7 strength
Combat 2 = -25% damage from ranged attacks
Combat 3 = +10 healing per turn while fortified
--All Combat units get +5 healing with discovery of medicine.
Marine 1 = no reduction in strength when attacking across river or from sea.
Marine 2 = while embarked, +7 strength and +1 movement
Marine 3 = while in enemy lands, +7 strength and +10 healing per turn
--All Marines get +1 movement while embarked with discovery of combustion.
Special Forces 1 = +7 when fighting in rough terrain (forests, jungle, hills).
Special Forces 2 = +7 when fighting against fortified units and/or units in a fort; and can scale sea cliffs.
Special Forces 3 = attack does not use movement point.
--All Special Forces units gain ability to move by Paradrop with discovery of advanced flight
Combat 4, Marine 4, Special Forces 4 = heal while moving