WI: No nuclear-powered submarines

[Slowpoke]

Originally Posted by Ak-84

These are technical not inherent limitations.

Five decades of technical breakthroughs won't change the laws of physics.

There's simply too much of a performance gap between nuclear propulsion and AIP to just handwave it all away.

The nominal rated power of the primary system in the Los Angeles class is 26 megawatts.

By contrast, current AIP systems are rated at around 300 kilowatts, 0,3 MW, while diesels produce about 4.000 hp, or ~3 MW (the Project 651 'Juliett' class SSGs had the highest rated diesel installed power at about 7,3 MW, 9,750 hp).

Since diesel engine development wasn't stunted by the appearance of the nuclear reactor, the only area with 'wobbly' numbers would be the AIP. The problem is that, even with those extra decades of development, I can't see them managing to squeeze more than 4 times the OTL number.

And that isn't a very good thing, since 1,2 MW still compares very unfavourably with nuclear power. Speaking of which, the nuclear plant directly powers the electric motor(s) driving the screw, whereas diesel engines are used for charging batteries (the AIP can do either). Which are another thing; larger capacity batteries take longer to recharge meaning more time spent snorkeling (or more fuel consumed by the AIP).

In this alternate universe, I simply can't see SSB/SSGs larger than the OTL Juliett and SSKs larger than the OTL Sōryū.There are physical limitations that simply can't be surpassed by merely throwing more time, money and brainpower at them.

[Riain]

SOSUS would be more effective against SSKs because while they are silent on batteries they do have to charge them regularly as well as having to make good time on occasion which probably means surface running at high speed.

Without the high transit speed of nuke subs, which reduces both logistic footprint and vulnerability, I think countries will make a greater effort to secure foreign bases than IOTL.

[Riain]

Originally Posted by Slowpoke

Five decades of technical breakthroughs won't change the laws of physics.

There's simply too much of a performance gap between nuclear propulsion and AIP to just handwave it all away.

The nominal rated power of the primary system in the Los Angeles class is 26 megawatts.

By contrast, current AIP systems are rated at around 300 kilowatts, 0,3 MW, while diesels produce about 4.000 hp, or ~3 MW (the Project 651 'Juliett' class SSGs had the highest rated diesel installed power at about 7,3 MW, 9,750 hp).

Since diesel engine development wasn't stunted by the appearance of the nuclear reactor, the only area with 'wobbly' numbers would be the AIP. The problem is that, even with those extra decades of development, I can't see them managing to squeeze more than 4 times the OTL number.

And that isn't a very good thing, since 1,2 MW still compares very unfavourably with nuclear power. Speaking of which, the nuclear plant directly powers the electric motor(s) driving the screw, whereas diesel engines are used for charging batteries (the AIP can do either). Which are another thing; larger capacity batteries take longer to recharge meaning more time spent snorkeling (or more fuel consumed by the AIP).

In this alternate universe, I simply can't see SSB/SSGs larger than the OTL Juliett and SSKs larger than the OTL Sōryū.There are physical limitations that simply can't be surpassed by merely throwing more time, money and brainpower at them.

That's right, and what's more AIP systems have been very slow to appear. Aside from Walter HTP systems when could AIP systems be introduced?

[sparky42]

In relation to Slowpoke's comment about Power Generation I think I read somewhere that even the most advanced NATO SSK's have a far more limited Sonar system due to both size and power issues.

Is there any basis to that and if so how would that affect things?

[sparky42]

Originally Posted by Riain

That's right, and what's more AIP systems have been very slow to appear. Aside from Walter HTP systems when could AIP systems be introduced?

What about the Stirling Engine system the Swedes have developed, could that be brought online earlier?

[Riain]

Perhaps, a quick look at wiki shows that it was kept in the background by other technology but Sweden and Japan have stirling subs by the late 80s. You'd think the US could get it online earlier if they had to.

Fuel cells are used in the Type 212 Uboats and Russian Lada class subs, but again they're late 90s technology, fuel cells came into thheir own during the space race so I don't know if they could do much any earlier.

But the fact remains that AIP will not allow a sub to cover 1000km in a day like nuke subs can and frequently do. The transit part of a patrol will inevitably take up a good chunk of the 60-70 days food and stores, limiting time in the patrol area. What AIP will do is allow a much greater scope for submarged operations compared to say the USS Barbel's 90 minutes at 25 knots or 102 hours at 3 knots.

[Slowpoke]

HTP has the relatively unfortunate habit of spontaneously combusting when looked at the wrong way. So that's a technological dead end.

Closed cycle diesels are simple to make, but, apart for submerged operation, don't offer any advantage over regular diesels. They're just as noisy and leave a long trail of exhaust bubbles.

Stirling engines are an even older concept, and have the advantage of high efficiency per fuel unit consumed. But they too are noisy (considerably less than diesels, though), have many moving parts (high maintenance) and don't produce that much power (each of the four Stirlings in the Sōryū produces just 75 kW).

MESMA is a very simple design, since it's basically a regular turbine with a chemical (burning rectified spirit and oxygen) steam generator attached (instead of a reactor's steam plant). It produces a lot of power (more than the others, 200 kW), but is inefficient and has a larger waste heat signature than the others.

Fuel cells are a design that couldn't have appeared on a large-ish scale anywhere before the late 70s, simply because the materials weren't there. You need several decades of materials research. IOTL, there has been a considerable push towards fuel cells, yet we still can't say that the technology is anywhere near mature. Power-wise, they're between the MESMA and the Stirlings (each of the Siemens cells in the Type 212 produces about 120 kW).

Originally Posted by Riain

What AIP will do is allow a much greater scope for submarged operations compared to say the USS Barbel's 90 minutes at 25 knots or 102 hours at 3 knots.

Pretty much that. Best case ATL scenario, you're looking at about a month's worth of submerged operations at a speed of around 9-10 knots (OTL is roughly the same, but at about 7-8 kts).

[Riain]

I don't know if HTP was really given a fair shake; Nazi Germany tried it, the British built 2 in the mid 50s, and the Soviets built one but the US chased the nuke route. I wonder what the US could have achieved with HTP if nukes looked like going nowhere, would their materials science which IOTL got us the likes of the Saturn 5 rocket be up to the task of taming HTP?

I think you're over-estimating the performance of AIP, I think they can crawl along at 3-5 kts for weeks which allows the batteries to keep a full charge so they can provide that 2 hours burst at 25kts. If sub Captains don't husband their AIP resources they'll run out just like battery charge.

[Slowpoke]

The poor performance of HTP in pretty much any propulsion setup (and, by "poor performance" I mean "catastrophic loss" see HMS Sidon and K-141 Kursk) makes me believe that it would have been dumped all the same, nuke or no nuke.

Originally Posted by Riain

I think you're over-estimating the performance of AIP, I think they can crawl along at 3-5 kts for weeks which allows the batteries to keep a full charge so they can provide that 2 hours burst at 25kts. If sub Captains don't husband their AIP resources they'll run out just like battery charge.

The Sōryū can officially cover about 6000 nm at 6,5 kt in AIP mode, the 212 and Scorpène are officially rated at three weeks submerged without snorkelling. Since real numbers are usually higher than officially stated (ex. the Los Angeles has a flank speed of ~31 kt, compared to the vague "over 25") I add a bit extra. And, in an ATL where AIP research is even more advanced than OTL, the postulated increase is quite reasonable.

[Riain]

Originally Posted by Slowpoke

The poor performance of HTP in pretty much any propulsion setup (and, by "poor performance" I mean "catastrophic loss" see HMS Sidon and K-141 Kursk) makes me believe that it would have been dumped all the same, nuke or no nuke.

Sweden acquired the rights to the Mk 12 "Fancy" torpedo which blew up the Sidon, developed it and used it successfully with no problems for 40 years, as did their export customers Denmark, Norway, Peru, Singapore.

The Soviets used HTP in the 53-57 21" and the 65 series 650mm torpedos for 50 years, and while the Kursk was sunk dozens and possibly hundreds of Soviet subs conducted thousands annd possibly tens of thouands of patrols did not sink. What's more catastrophic torpedo malfunction is suspected to be why USS Scorpion sank, so catastrophic torpedo malfunction is not limited to HTP torpedos nor dodgy navies like the Soviets.

Modern AIPs all seem to have volatile and vulnerable components. Closed cycle diesels have liquid oxygen tanks and were nicknamed "ciggarette lighters" by the Soviets, these are being offered by Germany but not yet taken up by annyone. Stirling engines also have liquid oxygen stored in cryogenic tanks. MEMSA has compressed oxygen stored at about 900psi, and fuel cells have LOX stored cryogenically outside the pressure hull. This seems to me to be a lot of effort to get an auxiliary propulsion system of 300-600shp, about 10% of the power of the electric motor.

But the real reason I keep harping on about HTP is power. From what I can tell, and am ready to be corrected, HMS Explorer and Excalibur did their 25kts on the power of their HTP AIP steam plant. This would imply an AIP plant making thousands of horsepower, orders of magnitude greater than todays hundreds of horsepower AIP systems which are for creeping along without draining the battery, yet still have to resort to the likes of LOX and ethanol stored outside the hull.

This to me shows why navies would persevere with HTP and that it is technologically possible.

[Riain]

Originally Posted by Slowpoke

The Sōryū can officially cover about 6000 nm at 6,5 kt in AIP mode, the 212 and Scorpène are officially rated at three weeks submerged without snorkelling. Since real numbers are usually higher than officially stated (ex. the Los Angeles has a flank speed of ~31 kt, compared to the vague "over 25") I add a bit extra. And, in an ATL where AIP research is even more advanced than OTL, the postulated increase is quite reasonable.

Soryu has officially 450hp of AIP engine power, even if it is actually double that, it's still only 900hp when the main diesel has about 4000hp and the electric motor 8000hp. So while the AIP allows the Soryu to cruise along at 6kts for 3 weeks it does not allow the Soryu to do 25kts to move into attack position and escape the counterattack, it's the fulkly charged batteries and electric motor which allow that. All the AIP does is free the sub from the battery creep/diesel snort routine to a large extent, even then during your average patrol the sub will snort a number of times to extend the life of thhe AIP fuel.

Just as a comparison a Type XVII U boat had an endurance of 5 hours at 25kts using the Walter turbine, this is vastly superior to the 1 1/2 hours of the USS Barbel at 25kts on batteries.

[TheMann]

Originally Posted by Riain

SOSUS would be more effective against SSKs because while they are silent on batteries they do have to charge them regularly as well as having to make good time on occasion which probably means surface running at high speed.

Without the high transit speed of nuke subs, which reduces both logistic footprint and vulnerability, I think countries will make a greater effort to secure foreign bases than IOTL.

It does have to be said that SSKs cannot do most of the things SSNs can, but logistics would not be a fatal flaw because of the advent of the submarine tender. The navies that base across the globe still would, but good SSKs can go a long ways. Australia's Oberon class subs got all the way to the Sea of Japan at some times, America GUPPY-rebuilt fleet boats went all over the world, it should be pointed out. I don't think no nuclear subs changes much, honestly.

[Cook]

Originally Posted by abc123

So, what if somehow, nuclear drive for submarines is never made and all submarines are still conventionally powered?

The problem is that power derived from nuclear energy was obvious even before a sustained nuclear reaction was achieved; it was clear that nuclear energy could be used to generate long duration energy and (most importantly) did not need oxygen to do so. That an explosion could be generated, and generated in a mass small enough to be lifted by an aircraft, was much less clear. Prior to Mark Oliphant’s trip to America in August 1941, developing nuclear power for submarine propulsion was the primary focus of the American nuclear program.

[Gunnarnz]

Originally Posted by TheMann

I don't think no nuclear subs changes much, honestly.

It might mean that the sea leg of the US strategic triad is carrier-borne, however. Building an SSB or SSG is possible (as has been proved historically), but they'd likely be less capable platforms than the SSBNs in OTL. As others have noted, this is less of a problem for the Soviets - their boomers conducted shorter patrols, and often closer to port as well AFAIK. It might also not be too much of an issue for the other nuclear powers, who are generally closer to their targets. But the US would need a great many more submarines to keep the same number of warheads at sea in the same places as OTL, given the range and speed restrictions of conventional boats in comparison. Insofar as the USN keeps a SIOP role at all, I'd expect it to be based around carriers; with the USAF gaining a correspondingly greater share of the target load. We might see air nuclear propulsion get a bit more interest, or Project Iceworm go a bit further before the problems overwhelm it.

[Riain]

Originally Posted by TheMann

It does have to be said that SSKs cannot do most of the things SSNs can, but logistics would not be a fatal flaw because of the advent of the submarine tender. The navies that base across the globe still would, but good SSKs can go a long ways. Australia's Oberon class subs got all the way to the Sea of Japan at some times, America GUPPY-rebuilt fleet boats went all over the world, it should be pointed out. I don't think no nuclear subs changes much, honestly.

The tender and forward base would be the partial strategic answer to the problem that SSNs solve by 25+ kt transits. II say partial because their proximity to the fighting, necessary because of the slow transit of SSK, would make them more vulnerable to attack than SSN bases which have tended to be well clear of any fighting IOTL.

That leaves the problem of outright performance in a tactical sense, as even the best AIP only make it easier for a captain to juggle his propulsion options.

[TxCoatl1970]

Just dealing with the OP--

Based on the Wiki article and so forth, I'm inclined to say subs have a lot shorter legs or are much more dependent on sub tenders. You still need them for UNREP, repairs beyond what the onboard machine shops can supply, etc whether subs have nuke plants or not.

Whether they're the ultimate strategic deterrent trucking around SLBM's as OTL is sort of tricky due to the endurance issues. Stealth would be improved, as long as you were cruising along on batteries.
Something like current hybrid technology might have been tweaked earlier say 1970's with more emphasis. IIRC the basis was the work the germans did in WWII on the U-boats.

To me AIP's seem stuck as niche auxiliary systems that might allow trickle-charging of the batteries without engaging the diesel main drives, using a snorkel, or depleting onboard oxygen.

One might see a lot more research into fuel cells and liquid-metal capacitors for much improved electrical storage and release but assuming linear progress is difficult b/c scientific productivity doesn't scale directly to more $$$ and time spent tinkering with it- e.g nuclear fusion.

I think of peroxide-fueled drives and shudder at them being corrosive, explosive, and touchy as hell under ideal conditions, much less field use for thousands of hours. YMMV. Fuel-cells with elemental hydrogen have their issues as well.

So, long story shorter, subs have a more tactical role. I like the idea a hull-down wolf-pack of SSP/SSK's acting like a captor mine to mission-kill a CBG just as they pop out of homeport to deploy.
However, the best thing to send against subs is either a LAMPS helo or another sub with better hydrophones.
That's why a couple of SSNs tag along with a CBG as underwater pickets to make sure no hostile subs get inside the perimeter.
Whether SSK/SSP's would be able to tag along with a Carrier Battle Group depends on how much you want to sacrifice stealth for speed.

[sloreck]

The problem with pre-deploying SSKs off Norfolk (or similar) is that it will take some time for them to get there, especially if they are trying to avoid detection, and this is unlikely to be a "normal" deployment pattern. That being the case, seeing any SSKs doing this would be considered a war indicator. OTL the USSR would need to move significant numbers of bombers and tankers to forward bases from their usual spots before an attack, as flying from their usual bases in the more "developed" areas of the USSR would not be practical due to range issues. Therefore one of the things that was tracked was the presence of significant numbers of these a/c at forward bases, this number bumps and everybody gets nervous. Even more so for subs than bombers, keeping large numbers forward deployed or feinting often is too costly in many ways.

Helos working in pairs w/dipping sonar are death to nukes, to conventional subs even one helo can be deadly with active dipping sonar...conventional subs just can't run fast enough for any length of time.

[BlondieBC]

Originally Posted by Riain

Fuel cells are used in the Type 212 Uboats and Russian Lada class subs, but again they're late 90s technology, fuel cells came into thheir own during the space race so I don't know if they could do much any earlier.

Fuel cells were considered or pre-WW1 submarines, but rejected for technical reasons. You could easily have fuel cells by WW2 if you are willing to accept the limitations and have a POD to secure funding for development. Initially, submarines were seen as submarines, not ships that fight on the surface. In these type of ships, fuel cells can make sense. Then by WW1, they had been transformed into surface ships that occasionally dived. Then in late WW2, the thinking flips back to them being submarines.

Now I am not saying they are destined to work well, but in a world where there are round battleships and submarines that travel on the ocean floor for Russia, we could see the technology deployed. Butterfly away WW1, and I can see Germany trying to build a few as a demonstration of technical prowess or Russia just trying another odd idea. This becomes much more likely if we assume sometime in the 1920's of the ATL that the UK would begin to take the submarine threat seriously and develop real ASW technology. Then we can move the return to submarines up a few decades.

To a very large extent, there is a 20 year funding gap on naval technology between the wars, and fuel cells show up shortly after WW2. So like radar, precision guided weapons, and metal monowing fighters, these items are delayed by at least a decade due to WW1. Germany early WW2 submarines are little more than WW1 submarines built around 4" larger torpedoes and stronger pressure hulls with other minor improvements. Like the Swordfish torpedo bomber, the reflect more an upgrade on WW1 technology than the technology that one would expect to see a generation later.

[Riain]

What were the technical reasons? Fuel Cells were thought of almost 200 years ago, but IOTL they didn't come into their own until the space race. In a lot of instannces things that were thought of aren't practical because the supporting technology isn't there, things like metalurgy or sealing technology or electronics. Do you know, other than funding and necessity impetus, what the holdup was with fuel cells? That is assuming there was one.

[BlondieBC]

Originally Posted by Riain

What were the technical reasons? Fuel Cells were thought of almost 200 years ago, but IOTL they didn't come into their own until the space race. In a lot of instannces things that were thought of aren't practical because the supporting technology isn't there, things like metalurgy or sealing technology or electronics. Do you know, other than funding and necessity impetus, what the holdup was with fuel cells? That is assuming there was one.

I read it in passing for general TL research, so the memory of the details are a bit vague. But when the first were working on submarines, someone (seems like France) test all possible power sources including fuel cells and steam engines. There were not real details, so I presume we are talking either tests in a warehouse on a mockup or a test basically sitting on the surface or submerged by a dock. Remember that submarines were built with gas engines where the fumes created death traps.

The main benefit was greater oxygen efficiency (not sure how, but would guess a fuel cell burns less oxygen per horse power than diesel). Diesel won out as better technology (Horsepower), but this was not issue. When the first tried the concept, they built round submarines, that performed poorly on the surface (tended to roll over). When the realized they could add the extra metal outside of the pressure hull and get a ship that performed well on the surface, then the amount of oxygen became less important and diesel won out. A lot of the improvement in speed from the early days to the WW1 subs was optimizing for surface combat and deoptimizing for submerged combat. If you look at the ship models over time, you will see ships that are fairly close on surface to submerged speeds at first. Over time, the surface speed and range improves pretty steadily and the submerged speed is flat to declining.

And when one looks at the lack of existence of true anti-submarine weapons before WW1, one understands why they evolved this way. And once the Allies master submarine warfare about 1943, we see a quick movement back to ships designed to be submarines not surface combat ships that can also dive. If you play with POD, you will see about 5-10 years after the UK becomes serious about anti-submarine warfare, we likely see some type of submarine appear designed to work underwater.