Speaking today before the Senate Armed Services Committee, CENTCOM commander Gen. Lloyd Austin talked up the idea of sending additional US ground troops to both Iraq and Syria for the war against ISIS, saying that there was a clear need for "additional capability" to try to take ISIS' major cities of Mosul, Iraq, and Raqqa, Syria.

Gen. Austin went on to say that his people have done analysis on how many more troops were needed and had made recommendations to the White House, but declined to tell the committee exactly how many more troops this would entail.

Exactly how many US troops are already in Iraq and Syria isn't wholly clear either. Last month, the Pentagon claimed 3,700 troops in Iraq, only to admit shortly thereafter that in reality there were "well over" 4,000 troops there at any given time. In Syria, the number is smaller, but has varied in different estimates.