Warning: I have forgotten what the unit is called, and don't have Civ3 on this computer so no way of checking 
Civ3 has two specialist troop types:
Marine (for transports)
Paratrooper/Airborne Infantry (for hellicopters)
Playability: There is very rarely a need (or even oportunity) to deploy both of these specialist troop types!
Realism: There is a blurring between Commando, Paratrooper and Marine operations. Transports operate Hellicopters, and deploy all unit types!
It seems to me that both Realism and Playability would benefit from merging these two specialist troop types into one.
Complication
Marines exist throughout history, whereas Paratroopers/Airborne Infantry exist only from WW2 (or Advanced Flight).
Solution
1. Merge both modern era units into the universal Commando unit.
2. Reserve Marine for age of sail, and have Marine upgrade to Commando.

Civ3 has two specialist troop types:
Marine (for transports)
Paratrooper/Airborne Infantry (for hellicopters)
Playability: There is very rarely a need (or even oportunity) to deploy both of these specialist troop types!
Realism: There is a blurring between Commando, Paratrooper and Marine operations. Transports operate Hellicopters, and deploy all unit types!
It seems to me that both Realism and Playability would benefit from merging these two specialist troop types into one.
Complication
Marines exist throughout history, whereas Paratroopers/Airborne Infantry exist only from WW2 (or Advanced Flight).
Solution
1. Merge both modern era units into the universal Commando unit.
2. Reserve Marine for age of sail, and have Marine upgrade to Commando.