User blog comment:AdvancedRookie/Activision hints at more frequent DLC and content variety/@comment-99.251.212.180-20120105193215/@comment-3967954-20120105212513

It usually depends the operation / military force in question. Special Forces (like the SAS) are likely to use Submachine Guns because a lot of their missions are CQC. If, for example, the mission was a hostage rescue inside a block of flats, you'd bring an SMG rather than a long-barreled AR.