Aluminum, magnesium and austenitic stainless steel are also non-magnetic. But they also have worse strenght/weight ratio than titanium.

All of the above are difficult to weld. This increasest the cost, which means fewer subs. So current submarines are made out of low alloy steel.

The USSR was the only country to build submarines with titanium hulls, a practice which ended with the Cold War.

And only one class the Alfa fast attack submarine the titanium hull was used more to reduce weight (Half the displacement of a comparable Los Angeles class US attack submarine) to allow it to be the fastest submarine ever constructed (double the reported speed of US attack submarines and most likely at least 25% faster than their actual speed) rather than because titanium is non-magnetic. All Alfa subs were decommissioned in 1990 and sold as scrap.

Yep, the Alfa was a strange design, Titanium hull, reduced to way below safe minimum shielding to save the weight, noisy as hell (like insanely noisy).

Basically designed as the submarine equivalent of an interceptor, get somewhere fast and open fire.

IIRC the top speed of the alfa was above the speed of the NATO torpedoes in use at the time.

Reported top speed. And it was seen as shocking enough to spur the investment into new torpedo technology.

https://en.wikipedia.org/wiki/Alfa-class_submarine#Impact

Like most fears over high-performance Soviet hardware though, the threat turned out to be overblown compared to the actual numbers build / operational state.

Yep, the Alfa also had a tendency to slowly kill it's crew from radiation exposure.

well thats what you get for putting a fast nuclear reactor with minimal shielding in a relatively tiny sub.

It was also used in the K-278 nuclear attack subs, but only in the inner hull so wouldn't have had so much effect on reducing magnetic signature. It seems I was somewhat miss-informed. Thanks for helping clear that up.

The K-278 was part of project 685/705 of which 2 subs were made the K-222 (PAPA) and K-278 (MIKE) both were prototypes PAPA used a full titanium hull and resulted in the Alfa class subs and the K-278/MIKE was lost with all hands with it being the only sub of it's class.

It was also used on the Sierra class (Project 945) of which at least two have been refurbished and remain in service.

Titanium allows an increase in dive depth but has no effect on speed.

The ship's total mass must be close to the mass of the water it displaces. Less mass spent on the hull means more mass spent on the reactor and steam plant.

The displacement is based on the volume of the sub not the mass. Basically the Alfa was a small and light sub with probably the "biggest" reactor in terms of power output for it's size. What you got is a sub with half the displacement of an LA class submarine with a reactor with equal power output which meant that you could strap on some really powerful engines. So half the displacement with about the same power capabilities means pretty much that you can double your speed.

mass = volume * density. Water has a (nearly) fixed density. So for any given displacement, less mass allocated to the hull means more mass allocated elsewhere.

Yes but the mass doesn't effect the volume of water displaced if you put in a hollow 10 cubic meter steel cube into water or a solid 10 cubic meter steel cube they'll both still displace the same amount of water which is 10 cubic meters.

BTW the density of the sub is also for the most part pretty much equal to the density of water.

The only times where it's going to be either greater or lesser than water is when it's doing a static dive or fast ascent.

When the sub does it's initial dive and takes on water into it's buoyancy tanks it becomes about the average density of salt sea water once that is achieved it can use it's diving planes (foreplanes) to adjust it's depth.

https://www.math.nyu.edu/~crorres/Archimedes/Crown/CrownIntr... was useful for me in correcting some myths about mass and density I'd learned.

Interesting. I knew the US used it in airframes and assumed they just used it a lot less in submarines but you appear to be right, thanks.

The CIA had to setup shell companies to buy titanium for the A-12/SR-71, making submarines out of Titanium didn't made sense for the US as it would be a waste of a "strategic material".

The soviets also had to use titanium in many applications that would require high end steel as they both had plenty of it (almost half the world supply at the time) and their steel industry was decades behind the west and they just could not make the required quality of steel alloys. The soviets ended up using titanium as a replacement and became quite good at creating titanium alloys and working with titanium in general the US would most likely not be able to produce a hull out of titanium (at that time) without investing way too much effort into building that expertise which would be pointless given the titanium resources they had and their ability to make steels which were as good or better for most applications. The soviets had to resort into using titanium for every thing from infantry armor plating to razor blades.

There are places in Crimea where the streetlights are made from titanium.

What I find particularly amusing is that Marvel Comics in 1965 introduced a Soviet enemy of Iron Man: Titanium Man (https://en.m.wikipedia.org/wiki/Titanium_Man) ... Funny how they were "accurate" in mimicking the preference for using Titanium vs.Steel in the USA/USSR arms race.

I wouldn't be surprised if the Soviets experimented with basalt fiber composite hulls at some point. I think they used it in some ballistic missile cowlings, anyway.

Basalt fiber is similar to e-glass fiber, but has greater stiffness.

I'm guessing they made a few small fiber-wound spheres and did a crush depth test on them, but the results discouraged further experimentation.

Are you sure they make them out of titanium to save weight? I have two anecdotal pieces of evidence: 1. I have a friend who does welding for the navy and was called in to replace part of the hull of a nuclear sub due to a very hilarious design flaw. It was >6" thick and took days to fill in... with steel. 2. I've read "Concepts of Submarine Design" which goes into great detail on the principles and systems of military sub design. The authors make the case that getting more weight is often a problem. This makes sense because every foot or air space needs to be displaced by more weight in the steel of the sub. So if they had a problem with subs weighing too little, they could just make them more spacious. And they're not very spacious.

Third anicdote; titanium is pretty expensive stuff. Online metals is selling a 3"x12"x12" piece for $1.7k. If your hull was 200' long, 15' in diameter you'd need $486M just for the raw titanium on the hull. That seems high just for the hull, even for a nuclear sub. Google is saying the whole thing is probably about $2B and I'd expect all the other stuff in there to cost a lot.

A naval yard is not paying small-lot retail prices for their materials.

The supply has something to do with the price and the USSR had no shortage of titanium, so the accounting in your example would have been valid only for one side of the iron curtain.

Making a sub bigger increases drag, particularly if you are making the frontal profile bigger.

What was the design flaw?