Photo: Thunderball 1965 Danjaq, LLC, & United Artists Corporation. All rights reserved
Mini Self Contained Underwater Breathing Apparatus
While on the mini sized properties required for a sea based battle with baddies, Bond was also furnished with a tiny air capsule that he would need to insert into his mouth to gain around four minutes of breathing time.
Just in case he didn’t have use of proper breathing apparatus, of course.
And it fit straight into a cigar tube.
It also saves Bond’s life three times in the movie.