Back in the 1960s, I remember seeing almost exactly the same illustration in a space book at the Huntsville library. It was for a rocket troop transport, one of those 1950s fantasy ideas that didn't have a snowball's chance of happening.

Sure, you can get a small number of troops to a distant land in a hurry, but at a very high price. You have to hope they arrive at the right location with no ill effects from space sickness (see the landing craft scenes from "Saving Private Ryan"). You can pretty well forget about a clandestine insertion - rockets tend to be pretty freaking loud. Maybe you'll eventually be able to refuel and reuse your transport, maybe not. If not, then the transport cost is very high, indeed.