"One fascinating limitation [...]" Sounds highly unlikely. The sub has a huge area across which to dispose of the waste gas, the volume can't be that high that

"One fascinating limitation [...]" Sounds highly unlikely. The sub has a huge area across which to dispose of the waste gas, the volume can't be that high that they need to release big bubbles at once. The chances of a satellite pointing at the right area of sea being able to detect even a metre-cross bubble against wave background ... I really can't see it. Perhaps they should blow bubble rings and disguise as a dolphin?