Hmm, I think qrtxian's winning.
I have another one:
In the Dark Avatar campaign I had to capture the planet Dithir (I think it's immediately after the one after where you have to plant spies on Dithir).
After bunkering down, barely surviving the Dread Lord's repeated attempts to wipe me from the map I worked my way up the tech tree until I could build a huge Battleship, packed to the brim with Doom Rays. Oh yeah!
So I bought one. It put me about 2000 billion credits into the red, and the maintenance payments crippled my ability to get back in the black (I'm a bit better at the economics side now), but I had a ship that could smack down any ship the Dread Lords through at me (due to that cheesy tie rule).
I grabbed a Ranged Troop Transport and the Battleship and pointed them at Dithir. At this point I realised that the Battleship o' Doom couldn't actually REACH Dithir for lack of support. *facepalm* (Sensing a theme emerging here? :/)
Okay, so Plan A: Build a starbase there to bridge the gap. Hmm. Looks like a single starbase won't do it. Okay, I could build a second one, but the odds are pretty small of ONE Starbase not being nuked by the Dread Lords before I can get there. But two? Scratch that plan.
Fortunately, for reasons unbeknownst to me, the Thalan seemed to have THRIVED under the Dread Lord onslaught. They had a planet that bridged the gap nicely. Also fortunately, the Thalan were happy to hand it over for the tidy sum of all I could afford plus a little more. If they hadn't... yeah.