Generals of the Revolution Game Piece Explanations

Caltrop=Infantry

ArmTor=Tank

Thresher=Sea Battleship/Aircraft Carrier

Fight Kite=Fighter Jet

Each piece can be upgraded per the number on their sides.  Caltrop from level 1-4 and all others 1-3.
Further more ArmTors can carry (up to 2) Caltrops, Threshers can carry (up to 4 units) Caltrops, (up to 2) ArmTors, and (up to 2) Fight Kites and the Fight Kites can carry 2 Caltrops or 1 ArmTor.  The Thresher can carry mixed units, ie. 2 Caltrops and 1 ArmTor, etc.
Below is a player aid from the game: