I'm wondering if all subs have identical dive times. If possible, could we compile all
this stuff together? Also, I do recall critical dive as being double air usage, but I
have yet to verify that.

Thanks for your help, I'll get my Junsen on the stop watch ASAP.

Red Zone - Flashing Lights for Low Air ~ 20-25 seconds.
Critical Dive - 180DP per second until you reach 24% of your DP.
Critical does not use more air AFAIK.

IJN
Vickers L3 - 120 seconds
Junsen Type-1 - 140 seconds
Kaidai-VIA - 160 seconds
??? (?)

US
O-Type (?)
S-Type (?)
Barracuda - 155 seconds
??? (?)

RN
H type - 110 seconds
Oberon - 130 seconds
P type - 150 seconds
??? (?)

KM
Type II - 105 seconds
Type VIIA - 135 seconds
Type VIIC (?)
??? (?)