I'm a new Heinlein fan and also an FTL (faster-than-light) fan. Did he write any books where FTL was possible? All the ones I've read so far have been intra-system (Sol) only.
- Methusaleh's Children featured an experimental FTL drive by one of the characters that was essential to the plot; in Time Enough for Love, its sequel the same FTL drive is discovered to also work as a time-travel drive.
- The Number of the Beast, The Cat Who Walks Through Walls, and To Sail Beyond the Sunset all have a universe-hopping device that serves as an FTL stand-in
- Starship Troopers involves FTL, as Michael indicated, the book doesn't really get into details.
- Tunnel in the Sky and, I think, Have Spacesuit - Will Travel and Starman Jones all involve FTL or similar systems, at least peripherally.
Number of the Beast. Based in a 6-dimensional space, you can instantaneously travel to where you want to go provided you know the proper vectors.
Starman Jones. The starship in question accelerated to the speed of light where it jumped elsewhere.
The Cat Who Walks Through Walls, To Sail Beyond The Sunset. Drive is size of a sewing machine case and can instantaneously place the vessel anywhere, anywhen, in any universe with a velocity up to the speed of light. Computer controlled and uses virtually no power.
Future History. In one of the Lazarus Long stories an inertialess drive is used to go FTL.
Possibly Starship Troopers and Citizen of the Galaxy...but I don't remember the references.
I believe Starship Troopers had FTL, but I am unclear as to how it works. The book dealt more with planetary assaults than with space travel. They were definately on other planets, though. Another book of his had "gates" to other planets, through which colonization expeditions proceeded.
I do not recall the title - please edit or leave a comment if you know it. It was Tunnel in the sky.