The MS-06F2 Zaku II F2 Type (Neuen Bitter Custom) 

The MS-06F2 Zaku II F2 Type was an upgraded version of the original MS-06F Zaku II introduced in the middle of the One Year War. The Zaku II F2 Type featured a Minovsky fusion reactor that was approximately 4% more powerful than standard Zaku's, a more heavily-armored torso that rendered projectile weapon attacks less effective at hitting the inner cockpit and reactor, and significantly lighter. The reduced weight made the mobile suit much more fuel efficient and granted it a greater operational time.
The Zaku II F2 Type could also be outfitted with a pair of solid rocket boosters on its backpack that could give it a brief but tremendous increase in overall thruster output. The combination of a more powerful reactor and less weight made the F2 Type a more agile and maneuverable combatant.