The number of active duty submariners is always a fluid number, being it's an all-volunteer service of the Navy. The numbers have always been historically small; the Submarine Force typically only comprises about 5-6% of the Navy's overall personnel.
In today's terms (assuming 300,000 active duty sailors), given the number of active submarines, newcon (new construction) boats, those who are in the training pipeline, and those in command / support units, the number is likely between 15,000 and 20,000.
It's important to understand that like most hazardous duty services, there are physical and mental requirements that must be met by all volunteers before actually being allowed to a submariner. The most obvious is claustrophobia; unless you're comfortable being in tight, cramped spaces for weeks at a time without seeing daylight (and most people aren't), being on a submarine crew isn't the best career option.
All the sailors in it die.
yes
About 2,555 US Sailors died in the war. This figure takes into account US Navy airmen and riverine sailors.
Submarine activity is very important to the security of the US.
The Australian war cabinet.
several
2,555 US Sailors were killed in the Viet War.
The periscope, and I believe they have a lot more than 2 mirrors.
Shanghai was one place that sailors were taken to, many from San Francisco.
He was a US Naval Submarine Officer.
Virginia class
Only one US submarine sank in World War One.