How many troops does the U.S. need in Afghanistan?

by Frederick W. Kagan and Christopher Harmer

Discussions about how many troops are needed in Afghanistan after 2014 have come to seem like a competition—I can name that war in 3,000 troops; well, I can name it in 2,500… The proliferation of numbers without any explanation of where they come from or what they mean is bewildering to anyone not deeply steeped in the art of military force planning. It’s opaque to almost all Americans, in other words, who have no way of making sense of what they are hearing.

But the numbers actually do come from real calculations (or they should, at any rate), and the American people deserve to know what those calculations are. AEI and the Institute for the Study of War have jointly released a product describing how to calculate the force requirements for keeping one single base in Afghanistan after 2014, concluding that it is not possible to do so with fewer than about 6,000 troops. That’s right—numbers like 3,000 or 2,500 are militarily infeasible and physically unsustainable. The military simply cannot perform the tasks required to keep one base safe and operational at those numbers.

Six thousand troops would allow the US to keep one base, but it would be a self-licking ice cream cone—unable to do anything but exist. At that manning level, the base would have no real ability to advise or assist the Afghan National Security Forces. Worse still, it would have no meaningful capability to conduct counter-terrorism operations. Acquiring those capabilities requires several thousand more troops. It requires, in fact, more than one base. That’s how estimates for the forces actually needed to conduct the missions the president announced at his press conference with President Karzai get into the range of 20-30,000 quickly.

We have presented all of our assumptions and work, describing exactly what functions need to be performed and what kinds of units (at what manning levels) are required to perform them. If there is a serious military option at 3,000, we would welcome a clear delineation of which functions are deemed extraneous and/or how they could be performed at half of our estimated force-level.

We are presenting no recommendations here. If the president has decided to withdraw all American military forces from Afghanistan, that’s his prerogative. We can debate the wisdom of that decision at another time. But the public debate should at least be informed by reality.

Christopher Harmer is a senior naval analyst at the Institute for the Study of War. Frederick W. Kagan is the Christopher DeMuth Chair and director of the Critical Threats Project at AEI.