What Submarine Matters predicted on 18 November 2017 "Argentine Submarine San Juan Likely Sunk With All Hands" has unfortunately been accurate. Three days after San Juan went missing Submarine Matters commented:
"Generally and unfortunately submarines that have been "lost" for 2 to 3 days have sunk with all hands."
[may have been lost due to] "fire, explosion, flood or escape of poison gas can also occur due to malfunctioning of a sub's lead-acid batteries or torpedo propellant or warheads."
Seawater probably entered the snorkel mast (on and in the sail/fin/"conning tower")
- then followed the yellow line (see cutaway diagram above) into the ventilation system
- then gushed down due to pressure and gravity to the third "Electric batteries" bank (which is second
from the left - below the yellow line)
- saltwater in contact with these lead-acid batteries then caused a buildup of hydrogen
- that exploded due to rising hydrogen levels and short-circuit sparks.
(Diagram courtesy several sources above via REUTERS and International Business Times).
"Eternal Father, Strong to Save" The Navy Hymn for Submariners