The design of the X-1 took a lot of calculation. The bouyancy had to closely match the ballast weight. The placement of the ascent and descent valves were critical. Beyond the ascent volume, there was additional volume provided for emergency lift and to float it high on the surface for ease of towing. I "took her down" in a lake once where the bottom was soft mud. When it came time to surface, the ascent volume didn't provide enough lift because I also had to overcome the suction of pulling the buckets up out of the soft mud. I filled it further, utilizing the emergency lift volume, but she still wouldn't budge. I couldn't effectively push it up, because the bottom was not firm enough to stand on. Marooned in a submarine on the bottom of a lake! It looked as though I would have to abandon ship. With a lot of rocking, pulling, and wiggling she eventually broke free of the bottom (just barely). Then I opened all the valves to vent the excess air volume to slow my ascent rate. It was a hoot.