The 14 Dumbest Things In Star Trek VI: The Undiscovered Country
5. Cloaking Plot Devices
SPOCK: Gas. ...Gas, Captain. Under impulse power she expends fuel like any other vessel. We call it 'plasma' but whatever the Klingon designation is, it is merely ionized gas.
UHURA: Well, what about all that equipment we're carrying to catalog gaseous anomalies? ...Well, the thing's got to have a tail pipe.
And thus, utilizing a surgically altered photon torpedo, the Enterprise is able to hit General Chang's invisible prototype Bird of Prey and — with the Excelsior — blow it to kingdom come.
Exciting... but does this make any sense?
Fans have long pointed out an error in the narrative: that it's Sulu's USS Excelsior that's established as "cataloguing gaseous planetary anomalies." They're right, but it's not the screenwriters being dumb. A brief deleted scene on the Enterprise contained this dialog:
GORKON: Your research laboratory is most impressive...
KIRK: Starfleet's been charting and cataloging planetary atmospheres. All vessels are equipped with chemical analytic sensors...
...which would have made clear that it wasn’t just Sulu’s ship which had this equipment aboard. But that's not the problem.
The real issue is it's clumsy. Nothing anyone does in the story works as a setup for this. In fact, it feels like someone imagined a way for a torpedo to home in on a cloaked ship, then went back and put in a couple of throwaway lines to rationalize it. It doesn't show our heroes being smart by figuring out a solution based on things that've happened in-story, they're just handed a solution that Spock conveniently remembers when the narrative requires it.
It doesn't feel earned.
And, in a franchise sense, the dumbest thing here is that it took so long for anyone to think about tracing a cloaked vessel’s exhaust in the first place.