Sealab 2021 Episode 20 - 7211 Episode Title:7211.Episode Description:A nuclear submarine crashes outside the station, and the crew of Sealab (in a rare occurrence) must work quickly to stop an environmental disaster from happening. The only "serious" episode in the show, this was an original episode of Sealab 2020 which was redubbed by the 2021 voice actors, with approximately half of the original episode's footage excised to fit the shorter running time. The end is also modified. The episode's title derives from the sequence number of the original episode its footage comes from.