Ammo, or ammunition, is what your gun fires in battle. Ammo costs credits or gold to purchase, depending on whether or not it is premium.
Premium ammunitions are sometimes reffered to as 'Prammo' or 'Gold'.
There are 5 types of ammo in World of Tanks Blitz. 3 of those types of ammo are premium rounds; Armor Piercing Composite Rigid (APCR), High Explosive Anti-Tank (HEAT), and High Explosive Squash Head (HESH or HE).
Armor Piercing (AP) Edit
Armor piercing shells are the default ammunition on most guns that aren't howitzers. They do the amount of damage shown as the gun's alpha damage (unless the default ammunition of the gun isn't AP). AP rounds will sometimes ricochet off the armor of enemy tanks when they don't penetrate.
AP rounds will shoot through obstacles such as fences and cars.
Armor Pietcing Composite Rigid (APCR) Edit
Armor piercing composite rigid shells have higher penetration values than AP rounds do, but do less damage. They are premium shells unless they are the default ammunition for the gun they are being used in.
High Explosive (HE) Edit
High explosive shells do the most damage of any shell in the game, along with HESH. They do splash damage, making them useful if you're trying to damage the modules or crew of a tank. They usually cost less than AP to purchase (unless you're using a howitzer), and travel slowly. High explosive shells do not need to penetrate the armor of an enemy tank to deal damage to them because they explode on impact, but do much less damage than they normally would.
Since HE rounds explode on impact, they won't shoot through obstacles such as fences and cars, unlike AP and APCR.