from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. One of several external or internal tanks fitted in submarines; when filled with seawater they allow the boat to submerge; when emptied using compressed air buoyancy is restored and the vessel rises towards the surface. Auxiliary ballast tanks within the pressure hull allow the submarine to be trimmed.
Sorry, no etymologies found.
Tolland immediately dove down and swam beneath the sub, running his hand carefully across the Triton's more important ballast tank – the negative tank.