What force would you use?

Inspired by enigmatic’s thread about historic military matchups, I’m inspired to ask a similar question.

If time travel were possible for men and materials, and you were given a chance to change history by affecting the outcome of a battle, what modern force or forces would you take?

The ground rules: No nukes. The military unit can only have what it can carry, and the only aircraft must be able to land without an airstrip or on a carrier. (Let’s call it a limitation of the device you are using to travel time.)

What force would have turned these battles?

[li]Gettysburg?[/li][li]The Battle of the Bulge?[/li][li]Waterloo?[/li][li]Hannibal’s campaign?[/li][li]Cannae?[/li][li]The Spanish Armada?[/li][li]Any others you can think of…[/li][/ul]