The UMP45 is used heavily by the Russian forces. It is moderately used by Shadow Company. It is also a randomly generated weapon for Task Force 141 members and is a starting weapon in "The Hornet's Nest" used by Gary "Roach" Sanderson with an ACOG Scope. It is also the starting weapon used by the player on the ground during the Spec Ops mission "Big Brother".
The UMP45 is immediately available from the start of the game in the First Recon class, and it thus available for Create-a-Class from level 4 onwards.
With user friendly iron sights, optics on this weapon are of questionable use. The Silencer is a favorable attachment for the UMP45 as the weapon's naturally high minimum damage allows for 3-hit kills regardless of range. This attribute makes the UMP45 ideal for those who prefer a stealthier approach.
The UMP45 is also a good candidate to combine with Hardline for a killstreak deployer (while using team-benefiting streaks such as UAVs and Counter UAVs). It is also popular for Rushing with Marathon and Lightweight. Stopping Power is not usually used because of the already high damage. But if someone wished to use Stopping Power with the UMP45 they would benefit from a two-shot kill from close range instead of a 3, in some scenarios this can mean the difference between life and death.
The UMP45 is also the only SMG to consistently one-hit-kill in Hardcore (except if the enemy is using Last Stand, Final Stand or Painkiller, or when firing through cover), which makes it a great gun to take on groups of enemies.
A lower rate of fire is the UMP45's primary weakness. At closer ranges the UMP45 can be overwhelmed by weapons with faster rates of fire, such as the MP5K. However, the slower rate of fire can be easily solved with the Rapid Fire attachment. Some players prefer to use Bling in order to have Rapid Fire to compensate the low rate of fire, and the attachment he/she desires. It should be noted that Rapid Fire will make less time for the recoil to settle down and thus increasing it, making it more difficult for long distance use.