Now I know what he meant.

It takes about an hour and a half to fly southeast on a Chinook helicopter from Bagram to Forward Operating Base Salerno in Khost Province. (I gave up on the prospect of a C-130.) During the flight. you unspool about 5,000 years’ worth of progress on the highlight reel of human civilization. The terrain is an almost endless chain of mountains, with virtually no greenery jutting out from the mountainface — just an ashy, arid, bleached tan color stretching out over the horizon.

Mostly that surface is uninhabited, even in the valleys. The population centers that do exist feature maze-like structures that cut into the hills with frail strips of single-story construction that wind around each other and stop abruptly.

I counted exactly three high-rise buildings in 90 minutes. The first time I saw a building with any color – a sharp blue – it jarred me into noticing how monochromatic the landscape is. That building, it turned out, was attached to a military outpost where we briefly stopped.

A Chinook is loud, tight and uncomfortable. About 25 soldiers, contractors and reporters — along with one stately bomb-sniffing German shepherd — strapped into either side of the helicopter’s belly. Our legs were bent into unnatural positions, thanks to the baggage stacked up in the center of the bird. Two other passengers were seated between me and Sgt. Clark — one of the Chinook’s gunners.

Before we left, I overheard a crew member tell Sgt. Schon, her counterpart on the other side of the helicopter, that there was a rocket-propelled grenade threat on the flight route. I looked at the German shepherd, Cinco, and considered his panting face to be good luck.

About a half-hour into the flight, I craned my neck, stiff as it was from my body armor, to look out the window behind me. I saw a mountain, swept almost entirely by a silky tan sand, its peaks maybe 20 yards away from us. It jutted up and down like a vital sign measured on hospital equipment — no subtle inclines, just sharp heights and severe drops. Yet the mountain looked smooth, as if a footprint was the most absurd thing it could encounter. I thought I was watching a scene that would be unthinkable to witness from the earth’s surface.

That thought evaporated when Clark opened fire. She let out three bursts, the second the shortest: da-rrrrruck-duck-duck-duck-duck; duck-duck; drrrrruck-duck-duck-duck-duck-duck-duck.

I jutted my head around, trying to see who she was firing at from the different available windows, but I couldn’t see anyone. A few seconds later Schon joined in: duck-duck-duck; da-rrrrruck-duck-duck-duck-duck-duck.

Whether the mountain hid our RPG threat I’ll never know.