Which figure of speech is used in this text?
Houston, we've had a problem here.
—Astronaut Jack Swigert, after an oxygen tank exploded on board Apollo 13

 - chiasmus
 - understatement
The text uses understatement, which involves deliberately representing something as less serious or important than it really is.
We've had a problem here is an understatement, since losing an oxygen tank could be catastrophic.