Hell,
three kids + mentors in arizona did it, why can't FIRST teams do it?
However, if FIRST wanted an underwater challenge, then they would be have the include a lot of stuff in the kit to make it a little easier, an airtight frame and propulsion systems.
Testing would be an issue too beacuse people probably have to be in the water to handle the robot. Imagine during the beginning of the year when build teams are assigned; Drive, Frame, Electronics, Programming, SCUBA

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