Torpedo depth is a Whitehead in Fiume supplied many of the world's navies, and it had trouble with depth control until it developed the " balance chamber " with pendulum ( pendulum-and-hydrostat control ).
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The balance chamber had water pressure push against a disk that was balanced by a spring . " The inclusion of a pendulum stabilized the mechanism's feedback loop . " This development ( known as " The Secret " ) was around 1868.