Robert Bowling, the Creative Strategist for Infinity Ward, decided to treat his Twitter followers today by posting a picture of MW3 Spec Ops. When asked what the gun shown in the picture was, Bowling replied that it was the Remington ACR. In case you didn't already know, the Remington ACR was featured in the MW3 gun leak a while back.
As you can see, the ACR is visible in the screenshot above. According to Bowling, the guy with the yellow helmet is a Juggernaut. A Juggernaut will be a Spec Ops enemy that will require more damage to kill.