Maybe “boots on the ground” only applies to the ground at sea level? I’m spitballing here.

A team of US marines and special forces landed on Mount Sinjar in Iraq on Wednesday to assess options for a potential rescue of of 30,000 Yazidi civilians threatened by Islamic extremists and worn down by hunger and thirst.

The forces flew in on V-22 Osprey tilt-rotor aircraft that can land vertically. They joined a small number of American special forces who, the Guardian has been told, had been on the mountain for some days. That team had been assessing the military and humanitarian situation and guiding US air strikes against Islamic State (Isis) fighters encircling the mountain…

Fleeing Yazidis have reported seeing small teams of American soldiers high on the northern flank. “We weren’t allowed to go near them,” said a man from Sinjar who was airlifted from the former base. “They were being guarded by the Kurds.”

Their mission: Find a way to get tens of thousands of weak, dehydrated, and dying people off a mountaintop (where the temperature’s well over 100 degrees, by the way) when there are well-armed barbarians waiting below. One option is to lead them down the mountain on foot and into Kurdistan by land, but that’s tricky. ISIS is down there, of course, and the road south to Kurdish territory would take them through territory held by the jihadis. Who’s going to do the fighting if U.S. “combat troops” aren’t available and there aren’t enough Peshmerga to shoulder the load? Another option is to forget the route into Kurdistan and go north instead — but that would take everyone into Syria, where U.S. troops would be reluctant to go for political reasons. Could the Peshmerga handle that alone or would they, as one U.S. official told the NYT, need Marine support?

Option two is to simply airlift everyone off the mountain. There are four Ospreys stationed nearby in Irbil plus some unknown number of U.S. and British helicopters. That’s complicated too, though. Someone would have to set up a security perimeter on the mountain for aircraft to land, and each aircraft would probably need a combat aircraft to accompany it in case it came under fire. The sheer volume of people needing rescue is another logistical challenge. An Osprey can carry 24 people; a typical Chinook can carry around 34, although apparently some models run bigger. Assuming everything broke right — a big, secure landing area, all aircraft loaded to capacity, and, say, 10 Chinooks participating in the mission — you’d need just shy of 70 trips to get 30,000 people down. Let’s hope there are still enough physically able Yazidis on the mountain to load the weak onto the aircraft too, or else you’ll need even more troops to help carry the infirm.

Total American troops inside Iraq at the moment, by the way: 1,000 and counting.