Vickers L3 - 120 seconds
Junsen Type-1 - 140 seconds
Kaidai-VIA - 160 seconds

data from old (archived) topic, I don't know if this still correct
http://fm.en.kupaisky.com/Community/Forum/Old/View.aspx?num=141765&searchtype=1&searchvalue=&sort=6&category=D07&thread=20&page=1 

One thing to keep in mind, is that the slow speed of the vickers (18-20 kts on the surface, roughly 17 submerged) make its 120 seconds of air seem to never last long enough.  I remember, before my acct was archived, that when I first played the vickers, I spent most of my time just trying to survive long enough to submerge and reach the enemy. The next class up, I had enough speed to submerge almost within my own start area and still reach the enemy.

Hi,
if I am not wrong, "silverxy" did a table for all nations, not sure if it's from ss1 to ss5.5 but I am sure there was a lot of info there. 

Best regards,

Adefesios

**EDIT** Found it in the test server discussion thread about SS dive times:

http://navyfield.com/Community/Forum/View.aspx?num=16046&searchtype=4&pagecount=0&searchvalue=silverxy&sort=5&category=C03&page1=1