For overpowered...
In Sins of a Solar Empire, a Space-RTS for the PC, there was a weapon you could build that would fire a Nuclear Missile at an enemy world.
Of course, it takes quite some time for the payload to reach it's destination on some of the larger maps, especially when the target is in a different star system. The longest I've ever seen it take was about 10 minutes.
Also, it can only fire it at planets you know are there. You can't fire blindly into space. You can set it to auto-fire, which will cause it to fire at any convenient target, and continue to do so once the lengthy cooldown has expired.
Let's say you're using a massive fleet to scout out new worlds, and you just happen to stumble upon a nice little planet occupied by your enemies. The weapon see this, and since auto-fire is enabled, it fires a nuclear warhead.
This warhead will take 10 minutes to get there. In those 10 minutes, you will...
-Obliterate all orbital defenses
-Wipe out the local population though planetary bombardment
-Resettle the planet with your own subjects
And just as things are getting started on your new World... BOOM! A nuclear warhead... YOUR nuclear warhead, flies onto the screen and smashes straight into your planet.