A quick post on the myth of Test Depth.

[ET2SN]

In the game, Test Depth is used as a normal tactic. Just consider that as you dive deeper, the water pressure increases. The water pressure not only acts against the hull, but also all of the piping systems, seals, and pumps that move it around. Since the game doesn't model sea pressure as more than a binary switch, the tactic stays valid.

Imagine you're buying a new car. You do your homework and find the model you want can get to 110 MPH. Once you buy it, are you going to try to drive from New York to LA and back at 110 MPH? Wouldn't that be foolish? To keep the metaphor going, its highly doubtful you would ever get close to commanding a ship if you had 40 speeding tickets on your record.

In reality, Test Depth is used to validate the ship as a whole. You go to Test Depth after an over-haul or heavy maint. to make sure everything works as rated.
In a combat situation, Test Depth really works against you. Primarily, it takes more high pressure air to launch anything out of the tubes as you go deeper.
Instead, rely on your cavitiation curve. If you can't go faster than flank, what point is there to going deeper once you're no longer making bubbles?

One last point to ponder-
The term Emergency Deep (150 feet) is based on two factors:
-Its deep enough to avoid a collision with surface ships when your ship control might be marginal.
- You can safely pressurize the fire fighting piping and hoses without relying on the trim or drain pump. Going deeper could mean rupturing a hose or getting your damage control teams air-borne.

[FPSchazly]

Thanks for the good info! I'm quite surprised stuff like needing more HP air for deeper launches was not included in the game. I guess they have to draw lines in the sand somewhere, huh?

[ET2SN]

Remember what I said about those seals.
The other end of the screw (prop) is bolted to the shaft which goes into the people tank to get turned by the reduction gears.
The shaft seals "clinch" tighter to the shaft as the pressure increases, so you also need more horsepower to overcome that friction. In other words, the deeper you go the louder you get in terms of ship-generated noise.

The one thing that has bugged me over the years, however, is the scope. Scopes rarely flood. The scope has the same rating as the hull in terms of Test Depth, it sees the same pressure as the hull and that's how it was designed.

Shessh, you'd think a 10 year old $20 game would get that right..

[FPSchazly]

Yes that is quite interesting about the scope. It is outside the pressure hull, isn't it.

I never thought about that regarding the shaft seals, though. That is a good point.

[Kapitan]

I did work out the air situation many years ago when researching the Thresher incident.

Thresher had a two part problem, her test depth at 1300ft had a profound effect on her blowing her ballast during her last emergency and here is why.

Thresher's ballast systems were from an old design taken from a diesel submarine which do not dive as deep (most SSK's hand around the 1000ft mk but the earlier stuff more 500-750ft) therefore her pipe work was of smaller diameter.

As explained above not enough air could get through under enough pressure to blow the tanks one of the lessons learnt in the thresher was the pipe work had to be increased from 2in diameter to 5 inch diameter (im on memory here)

The second part of the problem was the end of the pipe was a cage to filter out FOD being so deep meant that the temperature in the water was cold (being north Atlantic very cold) and moisture from the compressors iced over in the cages which created a blockage.

So how did thresher sink?

Simple naval reasoning: The vessel sunk due to lack of buoyancy

[ET2SN]

At one point during their construction, the Thresher and the Permit switched hulls.

What happened to the Thresher will always remain a mystery, more than likely is that Thresher experienced flooding due to a bad weld or a defect somewhere in her piping which then shorted out a large chunk of her electrical systems which caused a SCRAM which caused a loss of propulsion. The icing effect was documented because they could reproduce the effect during the later investigation.

That investigation led to the SUBSAFE program which made the Navy and the builders bite the bullet and stop assuming things were fine because that was how they were done in the past. Radiography (X-Rays of weld joints and materials) and materials testing went from doing a sample when ever it "felt about right" to every piece of steel that would experience sea pressure and every weld that would hold them together.

As you mentioned, the emergency air system was redesigned and updated to the modern emergency main ballast tank blow system that featured hydraulic controls with a manual backup and much sturdier piping.

The idea of running at flank bells at test depth probably came from Tom Clancy because the words sounded neat-o when he mashed them together. No Navy is that crazy.

[A-Ganger]

Originally Posted by ET2SN

- You can safely pressurize the fire fighting piping and hoses without relying on the trim or drain pump. Going deeper could mean rupturing a hose or getting your damage control teams air-borne.

The firefighting system is pressurized from a specific tank This tank is kept at a press. range for this and to provide flushing water for heads etc.

Firefighting on-board uses the same pressures regardless of sub depth, and the trim pump is (one method) used to fill the tank which of course adds pressure to it.