Successfully complete the indicated task to unlock the corresponding equipment:

Ambassador gunship: Successfully complete level 3 of the Helicopter Flying mission
Diplomat heavy tank: Destroy the targeted buildings for the Allied Nations. 
MOAB bomb: Successfully complete all HVT missions for the Allied Nations. 
Nuclear Bunker Buster: Successfully complete the final contract mission, "Get 
Solano Part 2" to unlock it for purchase from Eva for $1 million