[bewaretheirs]

It's tower on a large steel platform but it also includes significant GSE (ground support equipment) - cabling and cryogenic plumbing to connect to the rocket to let it be fueled and readied for launch, all connected via mechanical arms to pull the quick disconnects away from the rocket, in some cases into armored boxes to protect against the rocket exhaust. Plus a crew access arm to let astronauts board, elevators so they don't have to climb stairs in their space suits, etc., etc.,

It is carried around by one of the two existing crawler-transporters, which moves it between the VAB where the rocket is built and the launch pad.

[Animats]

What, this isn't even an new crawler/transporter? It's just the gantry and plumbing?

[bewaretheirs]

No need for a new one; the two they built for the Apollo program still work just fine.

Note that the crawler-transporter doesn't hang around at the pad during the launch - after setting the mobile launcher down at the pad, it drives away back towards the VAB until it's needed next.

During the Apollo era, it also transported the Mobile Service Structure - a tower with work platforms that allowed access to much of the spacecraft on top of the rocket.