It's not at 180 ft.
There was a lot more to the story than the show depicted. Once the first merchant vessel arrived they ran a cable around the stern of the sub to support it as it was still slowly sinking. After the crew was off, this cable was passed to a tug which could not budge the sub so another cable was rigged and passed to a battleship that arrived on scene. It had enough horse power to break it free from the bottom. (It was theorized that one of the bow planes had dug into the bottom and then finally snapped off and this was confirmed by salvage divers later.)
They then drug the S-5 along the bottom inshore to make salvaging easier but the tow cable eventually parted and a bouy was placed to mark the site. Still, if I remember correctly, it lies in about 130 ft of water, not 180 ft. They never bothered to clarify that point or mention that it had been moved before it completely sank.
The salvage diver blasted open the water tight doors to access the compartments during the salvage and noted the deck plates in the forward battery indicated a battery explosion that had been suspected by the crew. They never could seal the hull enough to refloat the sub and abandoned it on the bottom. I think it was used extensively for ASW training by the Navy.
The sinking it self was due to multiple failures. The early S-boats (there were four separate groups of different designs - not all S-boats were the same). The S-5 had separate port and starbord ballast tanks that used very hard to operate mannually actuated kingston valves. The result was that on the bottom it was impossible to get the ballast tanks in the bow completely blown without rolling the sub on it's side. This reduced the bouyancy available and also wasted high pressure air. The primary ballast pump failed and the smaller pumps were not rated for that depth or pressure.
The S-5 crew however made them work to some degree by blowing high pressure air into the torpedo room to reduce the pressure differential and allow the smaller pump to work and managed to get much of the water out of the torpedo room. The bad news was the pressure in the forward compartments assisted the chlorine gas from the flooded batterys in moving past the watertight seals into the aft compartments.
The main induiction valve was sticky but even though it was left open it should not have sunk the boat. The problem was that it was very difficult to close, espesially with the pressure on it from the incoming water. So what should have been a messy but non fatal flooding turned into a major problem.
To aggravate things the local induction valves in each compartment were screw actuated valves that were also very slow to close. If these could have been quickly closed the stuck main induction valve would not have been a problem. These local valves were changed as a result of the S-5 accident to a lever operated quick closing valve that could be easily closed against incoming water pressure.
The naval historian they interviewed had a pretty negative attitude about the S-boats in general. The early S boats were very much developemntal boats with S-1 thru S-3 being of three separate designs with two types receiving orders for production and additioanl development. He was correct that one of the diesel designs used in a few S-boats vibrated badly, but omitted that there were three separate types of diesels used in S-boats and that the poorly designed diesels were replaced in the boats originally equipped with them. Most of the S-boats had long careers and several served in the first 2 years of WWII. They were by that time small, cramped and overaged compared to the newer fleet boats and called "pig boats", but he seems to have let that color his judgement about was actually a successful post WWI class of submarine.
They did talk to the author of "under pressure", but geez with a little research or if they had actually read the book they could have found a whole lot more interesting objectives for the dives. There has also never been any mystery about the sinking. And the "revelation" that the chief of the boat forgat to close the main inducton was not arevelation at all. It was known to the court of inquiry and was public knowledge at the time, but the blame was rightly focused on the mechanical defects in the S-5.
