The M119 is a lightweight 105mm howitzer used by US forces. It is a licenced copy of the L119 light gun which is used by the British Army, the M119 as several modifications including a more advanced fire control system than the L119, it can also fire most of the standard NATO ammunition.
In Armed Assault the M119 is used by US forces, it is a static weapon and can't be moved and can only fire HE ammunition. There are 2 positions on the M119, a gunner who is able to fire the gun and an obeserver who is able to spot targets. If two of your AI controlled characters mount an M119 in both positions the option to oder a fire mission becomes avaliable, these are only good if you know the precise location of enemies.
The M119 has very little anti-armour capability, it takes 4 shots to destroy a T-72 and a T-72 can easily take out an M119 in one shot. It is only really usefull against enemy personel although it is sometimes used as an anti-aircraft gun but this requires a bit of skill to hit a moving helicopter.