Okay, I have been doing a lot of practicing with SMG's and have stumbled on some usefull tactics for them in game.

Ahem, Sub Machine Guns are accurate at close to medium range 0-50 yards in game, they are best used by a player who is supporting others who have Rifles(M4) which are primarily medium to long ranged.

If the enemy outflank (go around) the Rifle carriers they generaly have a good chance at killing them so a weapon such as MP5 or P90 when used to guard the riflemen can be very effective in this situation, the SMG should be used in controlled 2-4 bullet bursts at medium range and full auto at close range.

The Tactic of "Rushing" is best accomplished with a P90 or equivelent, its large ammo clip and high rate of fire means you can take 3 or even 4 enemies out before thinking about reloading which is also a speedy process. In order to be efficient with an SMG aiming is a priority, at close range upper chest and head are the obvious choices, at medium range and static however the best course of action is line up cross-hairs with your enemies head and as you fire and then bring the cross-hair down to your enemies feet while firing. Sounds silly but the recoil of the gun makes the bullets tragectories gradually rise but not the cross-hairs.

On a moving target more deflection aiming is needed than with an assault rifle ie; aiming further ahead of your targets intended route, this mixed with the recoil compensation should ensure a kill.