The key word here is likely rapid. Doing a suborbital hop is much faster than going through atmosphere, because you get to accelerate to much higher velocities. Even supersonic planes take forever to get anywhere, while a suborbital hop would let you get to any place on the planet in under 2 hours.

There never was a space shuttle sitting around ready to launch on-demand though. A 2 hour travel time is irrelevant if it takes weeks to prep for the mission.

The space shuttle could also only land at a handful of runways on the planet.

And everyone on the planet would know you're doing it via national television or every inter-continental ballistic warning system?

I don't agree with the use case but to play devil's advocate, not every actor would be able to do something about it.

I’m having a hard time finding the source, but a mission requirement of the Space Shuttle was something along the lines of “Deploy a dozen marines to Moscow in less than 1 hour.”

Yeah, that's just mythology. The concept doesn't work out.

The shuttle did have a military requirement: the air force wanted to be able to launch into an orbit over the south pole, then up across Russia from the south, to return and land after that single orbit. That pretty much forced the use of wings that could glide, vs capsule style re-entry, and opened the path to most of the shuttle's design flaws.

As for why the air force wanted this, the presumption is surveillance, but I don't think they've ever officially answered, other than denying that they ever considered a bomber mission for the shuttle.

IIRC the requirement was to be able to snatch a Soviet satellite & land wit it in less then one orbit. Here it is demonstrated in KSP (with a SSTO, not shuttle though): https://youtu.be/pFCQEgnKwdY

On the other hand Soviets were reportedly scared to death of shuttle starting on a "normal" mission only to use it's wings and heat shield to dip into the atmosphere and change it's inclination, so that the new orbit passes directly over Moscow, from an unexpected angle. Then it would drop a 20 ton worth of RVs with nukes in a decapitation strike without any warning.

It is estimated that this is one of the reasons why the Energie & Buran program were started - they also wanted part of the "fun".

Maybe somebody wrote a requirement about that once, but it doesn't sound very practical. I know they were dreaming up a lot of fanciful things when they were setting the requirements though.

I think the actual shuttle had a life support capability for like 7 people. Not sure of the actual flight crew requirement, there's probably room for like 3-4 other guys. It can land on a runway, but it's gotta be really long, and there's only one shot, and it'll be really obvious and has no ability to evade defenses. No chance of it landing in Moscow unless the Russians let it. And then you'd be in the middle of a huge military base or something, and what are 4 guys going to do except be killed or captured immediately.

Maybe they could get there in an hour. From a specific launch pad in Florida, and if the shuttle is all set up to launch, which takes months. And it'll be blindingly obvious to everyone in the world that something just launched heading straight at Moscow.

You could put a crew module into the payload bay. Also the Shuttle's life support systems were designed for multi-day missions so they may have been able to handle a two hours flight with more people.

There were seven people aboard the Challenger.