![](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjapYr_oA5umrUB4clqbzSehBx7yn2PE4mBWVwcyNzZ0vdJfs1e6I9zhVY0DIWMMGDAXQ5htmW71n6Q49RNBwppjtbdzD7Uba5JHTxkUy-NLLpHZL3mpE-qeYB_OK9d60Ip_CiM/s400/submarine-barometer-manometer.jpg)
WWII submarine barometer-manometer. These ranged up to 37 inches of mercury, mainly because BEFORE a dive, the interior of the sub was slightly pressurized, to ensure that valves, hatches, and of course any bullet holes were sealed off. A leak in a diving Submarine could be fatal.These were mounted prominently BETWEEN the two"PLANESMANS" stations, as these crewmembers could cancel a dive if this instrument did not show a pressure build up in the hull.