These submarines are used for access to and around the giant underwater base of Bob the Killer Goldfish on the aquatic planet La Planeta de Agua (Arriba!). Jim uses at least three submarines to access different areas of the base in his search for the nefarious mastermind, often down dangerously narrow rock passageways.
Although the submarines have clear glass domes that can withstand the water pressure, unfortunately they are liable to begin to crack given too much impact damage. If they crack too much, they will implode, instantly killing Jim. Although there are refueling rods at various places to pump oxygen into the submarine, these must be used regularly, since the submarines cannot hold more than two minutes' worth of air at a time. Running out of air will also cause them to implode under the water pressure.
There are a few treks in the submarines through Down the Tubes, these are relatively short journeys, with plenty of air-pumps. Down the Tubes takes place mostly within the interior of the base. However, the second section, Tube Race, takes place mostly outside the base for a long and difficult submarine ride.