Unlocks:
Sniper Rifle Range mini-game:
Successfully complete Campaign 1.

EMP Cannon Range mini-game:
Successfully complete Campaign 2.

Cow Bouncing mini-game:
Successfully complete Campaign 3.

Assassination mini-game:
Successfully complete Campaign 4.

Hint: 
Long distance shot:
Use the sniper scope to zoom in on distant enemies, then shoot them with the 
unguided rockets or cannon even without a lock. 

Surprise kill:
Stay below a hilltop, hiding from enemies, rise up, fire a few rounds, then dip back 
down to avoid return fire. 

See enemies easily:
You can also use the thermal scope during the day to clearly distinguish vehicles 
and soldiers. 

Saving missiles:
Shoot fuel barrels and other explosive objects that are next to targets with your 
cannon to get extra damage without using missiles. Save your guided missiles for 
other helicopters. 

Level 1: Easy kills:
After you go threw stealth training and go back to the base it will be under attack. 
When you reach the front of the base enter stealth mode. Stun the tanks, half 
tracks, and jeeps, then shoot the men.