The soldiers of NEMO don't just rely on swimming and lung power to get around; a variety of jet-propelled apparatuses for combat and reconnaissance are utilized when complete stealth is not needed. And larger vessels, such as the Type-57, are used for maintenance and heavy lifting in deep-sea environments.
But alas, it is not fullproof, and susceptible to being blown apart by underwater firearms. Now cadet-55417, Maki, is alone almost 100m below the ocean surface, with no rebreather to use.