As mentioned in the video, candles are a backup/supplemental form of oxygen generation. Older platforms will have an AEOG (Automated Electrolytic Oxygen Generator), popularly known as "the bomb", and newer platforms will have the substantially safer LPE (Low-Pressure Electrolyzer).

Burning candles is a hassle and creates a big mess, to the consternation of junior enlisted who have to haul clinkers around and clean up the constant dust storm they leave behind. That said, huffing that good O2 straight out the spout will keep you awake, especially if your boat has been below 18% for awhile.

I remember A gang telling me how explosive the whole AEOG process was when I checked in. It literally is a potential bomb.

They used to be worse! The original 6L16 EOG didn't have the "A". It was neither Automated nor Advanced, the only "A" it had was operated by A-gangers!

3k-lbs of pure O2 combined with a reputation for fires, rapid depressurizations, and hydraulic leaks. More than one auxiliaryman got blasted to bits by those things back in the '60s. Every submariner thinks theirs is a unique and special hell, but I don't envy those who went underway with the old O2 plants.

At the end of the movie about the Kursk, someone drops one in water accidentally and it seems the air ignites afterwards. Are these candles the same thing?

That was a potassium or alkali metal oxide that reacted with the salt water and exploded

Potassium superoxide which acts as an CO2 scrubber, oxygen generator and dehumidifier in one. It reacts violently with water, and since it produce massive amount of heat and oxygen, it will also cause an explosive fire if the reaction occur near a fuel.

In Kursk it is suspected that it got dropped into water that had a lot of oil floating on top.

I just watched that today! Super interesting set of videos. I highly recommend watching them.

I'm kinda torn on this. On one hand it's super interesting, on the other it's state-sponsored army propaganda series, luring in young Americans, painting everyone in service as a hero.

Oh no, a clearly labelled piece of entertaining advertisement, how awful.

Also... even these show how difficult life on a submarine is (and the ultra-wide angle used most of the time shows how extremely claustrophobic everything is). Not exactly appealing. It takes some very special people to do this kind of job, and I doubt a lot of people are cut out for it...

You underestimate how big a role the "cool factor" plays in recruitment. Note how propaganda always focuses on jets and tanks and submarines and aircraft carriers and futuristic gadgets, and when they do feature an soldier it's always a badass tier-one operator who gets to flaunt the uniform code. Seventeen-year-olds don't get so excited about the prospect of burning literal shit in a hole behind some godforsaken checkpoint in Afghanistan until one day an IED takes their leg off.

I was in a different branch but I feel like the series was probably a remarkably balanced portrayal of Navy/submarine life. There's a lot of cool stuff to talk about but clearly it's a demanding job and most of those sailors looked worn right out.

Most interesting part for me was the basically continuous education aspect for everyone on board, as well as the very frequent drills. I guess a combination of keeping people educated/trained and avoiding idleness in such an environment for months at a time.