[LukeFF]

Originally Posted by Ducimus

The qualification time as i understand it, was "under a minute" or 50 seconds, depending on what source your reading. That being said, with extra work and training, a fleet boat could be brought to periscope depth in as little as 30 to 35 seconds. Diving a fleet boat, by one account, is an art form.

According to the Fleet Submarine Manual, the minimum time was 60 seconds:

A quick dive is made when the ship is underway on one or more main engines. The bow planes are placed on FULL DIVE and the forward speed results in a maximum downward thrust on the bow planes. As the submarine submerges, the upper surfaces of the hull and superstructure act as planing surfaces and increase the downward thrust. The quick dive is the fastest of the three types and is used in acceptance trials of new submarines, when it must be executed within 60 seconds from standard diving trim.

http://www.hnsa.org/doc/fleetsub/chap18.htm#18A