Boats could go passed the "test depth" on the dial, but how much more, or for how long? If you find out, you won't be surfacing.
That is how TMO is set up. I've taken a Balao boat down to almost 700ft, and made it back up after the DDs were done trying to ruin our day.
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A legislative act contrary to the Constitution is not law.
-John Marshall Chief Justice of the Supreme Court
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