Better breathe your oxygen, just in case.
4 seconds sound clip from the The Atomic Submarine movie soundboard.
You can hear this line at 00:49:59 in the DVD version of the movie.
Quote context
[...]
- Ready to open air lock door, Captain.
- What do you say, Doctor? Shall we take a chance?
- You all stay here. I'm gonna take a look inside.
- Better breathe your oxygen, just in case.
- Air, pure air, under pressure.
- Well, we won't need these tanks.
- The bow drilled through her, but she sealed herself right up.
[...]