Here is the full list of all 11 Gunhound EX achievements.
Acquire the 35mm AA Autocannon
Cleared all Simulator Missions
Acquire the 30mm Autocannon
Acquire the Gatling Claw
Acquire the XVI Naval Cannon
Acquire the Napalm Thrower
Acquire the Clutch Fang
Acquire the Shotgun
Acquire the Grenade Launcher and Hand Grenade
Acquire the Anti-Ship Energy Cannon
Maxed out the Score Counter