Future Heavyweight Torpedo Development

Bruno Anthony

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It seems that new sub launched heavyweight torpedo development is fairly static. USN is up to the seemingly 9th mod of the Mk 48. Also looks like they picked the wrong motor for the Mk 48 but that could be another topic.
 
There's really no need for a new clean-sheet torpedo design when updated mods/TIs already bring new capability to the weapon. A torpedo isn't particularly complex.

looks like they picked the wrong motor for the Mk 48
Not entirely certain what you mean here?

Honestly, despite what video games may say--modern HWTs (from all countries really) are remarkably lethal. If you get shot at, you're probably dead. (So don't get shot at.)
 
There have been some rumors that they might switch the next iteration of Mk 48 (or successor) to electric rather than the swashplate IC motor in the current version. High energy density batteries like lithium ion are becoming a credible alternative to Otto fuel.
 
It seems that new sub launched heavyweight torpedo development is fairly static. USN is up to the seemingly 9th mod of the Mk 48.
Not sure how much of the original Mk48 is left, to be honest.


Also looks like they picked the wrong motor for the Mk 48 but that could be another topic.
How so? The otto fueled weirdness works pretty well. (It's basically a hydraulic motor but running on external combustion)

The UK Spearfish runs on otto fuel as well, it's just a small gas turbine instead.



There have been some rumors that they might switch the next iteration of Mk 48 (or successor) to electric rather than the swashplate IC motor in the current version. High energy density batteries like lithium ion are becoming a credible alternative to Otto fuel.
Disagree, the electric torpedoes are slower and shorter ranged. And that's usually running silver-zinc batteries which have equal or better energy density to Lithium batteries! The only advantage lithium has over AgZn in batteries is rechargability, which only matters for exercise torpedoes. On the other hand, having rechargeable ExTorps is not a bad thing.


About the only way you could pull more performance out of the torpedo is to shift to the same stored-chemical propulsion as on the Mk50 LWT, sulfur hexafluoride and a block of lithium driving a steam turbine. The advantage being that sulfur and lithium fluoride take less volume than SF6 and Li, so there's no exhaust to have to pump overboard.
 
Disagree, the electric torpedoes are slower and shorter ranged. And that's usually running silver-zinc batteries which have equal or better energy density to Lithium batteries! The only advantage lithium has over AgZn in batteries is rechargability, which only matters for exercise torpedoes. On the other hand, having rechargeable ExTorps is not a bad thing.

Whatever happened to Aluminum-water batteries?

"Recently acquired by major tech firm L3 Technologies, OWP has developed a novel aluminum-water power system that’s safer and more durable, and that gives UUVs a tenfold increase in range over traditional lithium-ion batteries used for the same applications."

See:

https://news.mit.edu/2017/batteries-drink-seawater-long-range-autonomous-underwater-vehicles-0615
 
Not sure how much of the original Mk48 is left, to be honest.



How so? The otto fueled weirdness works pretty well. (It's basically a hydraulic motor but running on external combustion)

The UK Spearfish runs on otto fuel as well, it's just a small gas turbine instead.




Disagree, the electric torpedoes are slower and shorter ranged. And that's usually running silver-zinc batteries which have equal or better energy density to Lithium batteries! The only advantage lithium has over AgZn in batteries is rechargability, which only matters for exercise torpedoes. On the other hand, having rechargeable ExTorps is not a bad thing.


About the only way you could pull more performance out of the torpedo is to shift to the same stored-chemical propulsion as on the Mk50 LWT, sulfur hexafluoride and a block of lithium driving a steam turbine. The advantage being that sulfur and lithium fluoride take less volume than SF6 and Li, so there's no exhaust to have to pump overboard.

Shoot, I got two different things confused.

Electric was, I think, a suggestion for the RAPTOR low-cost torpedo. Basically a reversion to a two-torpedo inventory with a less expensive anti-surface torpedo to fill out the inventory while ADCAP remains as the high-end weapon mainly for ASW.

The other is Mk 48 Mod 9, which actually is proposing to replace the Otto fuel engine with SCEPS.

https://www.highergov.com/budget/mk-48-adcap-f4adcde/
 
Whatever happened to Aluminum-water batteries?
I don't think those have the discharge rate that AgZn or Li do. So they have great range but bad speed. Good for recon UUVs, bad for torpedoes.



Electric was, I think, a suggestion for the RAPTOR low-cost torpedo. Basically a reversion to a two-torpedo inventory with a less expensive anti-surface torpedo to fill out the inventory while ADCAP remains as the high-end weapon mainly for ASW.
Something the size of a Mk37 would be good for subs hunting skimmers. Half the length of a Mk48 so you can stow two of them in the same space.

Because the killer to submarines going to the happiest hunting grounds in the SCS/ECS/YS/SOJ again is lack of weapons per boat. A 688 or 774 only carries like 24 or 26 torpedoes. Add 3 more if you load the tubes. (you need an empty space to move things around) Now you need to leave a weapon or two in reserve to get home, so you're back down to that roughly two dozen shots at all targets.

But with half-length torpedoes you can stick 36ish antiship with 8ish Mk48s, or whatever your magic ratio works out to be.


The other is Mk 48 Mod 9, which actually is proposing to replace the Otto fuel engine with SCEPS.

https://www.highergov.com/budget/mk-48-adcap-f4adcde/
Ah-ha!

And with SCEPS, you wouldn't have the hot-run atmosphere contamination issue like you do with otto fueled torps. Instead, the drill folks would have to come up with some other new way to torture sub crews.
 
There's really no need for a new clean-sheet torpedo design when updated mods/TIs already bring new capability to the weapon. A torpedo isn't particularly complex.


Not entirely certain what you mean here?

Honestly, despite what video games may say--modern HWTs (from all countries really) are remarkably lethal. If you get shot at, you're probably dead. (So don't get shot at.)
Price-wise they appear very complex. About $1mil + for a late model AMRAAM vs $5mil + for a late model Mk 48.

From what I’ve read (one example: https://archive.navalsubleague.org/1984/the-antiship-torpedo) the swashplate piston engine on the Mk 48 chosen over the turbine which would become essentially the Spearfish engine is or at least was noisy enough to be a detriment if under ice, close quarters combat became the game plan. Granted it wasn’t originally designed for that like AIM-7 wasn’t designed to shoot down hard maneuvering fighters.
 
How so? T
Wasn’t the Mk 48 engine considered loud enough that in close quarters it would be a detriment as it would immediately alert its target? Wasn’t there a STEP Stealth Torpedo upgrade/replacement mentioned along the way?
 
Wasn’t the Mk 48 engine considered loud enough that in close quarters it would be a detriment as it would immediately alert its target?
Outside my knowledge, I was boomers only.


Wasn’t there a STEP Stealth Torpedo upgrade/replacement mentioned along the way?
If there was, I missed it. Got out in 2006.



Aren’t these boats equipped with powered torpedo reload systems? How many can be guided at once and against how many targets?
They do, but you can only guide one weapon per tube via the wires. Then you get to spend a couple minutes at an awkward down bubble to slide the tube-end of the wire spool out of the tubes before you can reload the tube.
 
They do, but you can only guide one weapon per tube via the wires. Then you get to spend a couple minutes at an awkward down bubble to slide the tube-end of the wire spool out of the tubes before you can reload the tube.
I phrased it wrong. I meant if you have say 4 loaded tubes, can you fire all 4 torpedoes and guide them at 1,2 or 4 separate targets?
 
I phrased it wrong. I meant if you have say 4 loaded tubes, can you fire all 4 torpedoes and guide them at 1,2 or 4 separate targets?
I ... don't actually remember now (where's that embarrassed emoji?). You can certainly fire 2 and guide them at one target. Only 1 tube per side at a time, though, due to how the impulse pump is set up.

But that's also with what is the old BQQ6 passive-only sonar and Mk91(?) FCS, not the new BYG unit.
 
Price-wise they appear very complex. About $1mil + for a late model AMRAAM vs $5mil + for a late model Mk 48.

From what I’ve read (one example: https://archive.navalsubleague.org/1984/the-antiship-torpedo) the swashplate piston engine on the Mk 48 chosen over the turbine which would become essentially the Spearfish engine is or at least was noisy enough to be a detriment if under ice, close quarters combat became the game plan. Granted it wasn’t originally designed for that like AIM-7 wasn’t designed to shoot down hard maneuvering fighters.
Note that that article is 41 years old and from the Sub League newsletter--they'll publish articles from any rando scrub so don't assume there's much due diligence or genuine expert commentary in them. Some of the assertions in that article are pretty silly.

Torpedoes have grown quieter over the decades but there is no torpedo on Earth that you could genuinely consider "quiet" at full speed. They run at very high RPMs and they really aren't large enough for the extensive isolation you'll find on submarines. It isn't really a problem though, because torpedo seekers are highly directional and aren't really susceptible to self-noise.
 
Note that that article is 41 years old and from the Sub League newsletter--they'll publish articles from any rando scrub so don't assume there's much due diligence or genuine expert commentary in them. Some of the assertions in that article are pretty silly.

Torpedoes have grown quieter over the decades but there is no torpedo on Earth that you could genuinely consider "quiet" at full speed. They run at very high RPMs and they really aren't large enough for the extensive isolation you'll find on submarines. It isn't really a problem though, because torpedo seekers are highly directional and aren't really susceptible to self-noise.
I see some prominent names when you use their search feature
https://archive.navalsubleague.org/
As for that particular article, it’s old but it’s about the origins of the Mk 48 which is an old story.

What I’ve read is that the main concern about the Mk 48 especially in arctic warfare which because of the sound conditions would require getting in real close, firing a 48 would be the submarine pulling its pants down and giving away its location. They didn’t know about it then but that’s where the Soviet rocket torpedo may have ended up with 1:1 kill ratios.

And apparently there were concerns too that the 48 under ice May go after the ice.
 
What I’ve read is that the main concern about the Mk 48 especially in arctic warfare which because of the sound conditions would require getting in real close, firing a 48 would be the submarine pulling its pants down and giving away its location.
Truth be told--especially back then the whole "shooting a torpedo will give you away" narrative is mostly a bunch of Clancyesque nonsense. Unless you're dealing with a adversary that is 100% alert and expecting to be shot at, you'd be surprised at what they miss.

They didn’t know about it then but that’s where the Soviet rocket torpedo may have ended up with 1:1 kill ratios.
I'm not certain who is claiming a 100% kill ratio, but unless you're very close in shallow water you're never hitting a submerged target with a supercavitating torpedo.
 
but unless you're very close in shallow water you're never hitting a submerged target with a supercavitating torpedo.
Isn’t that what arctic sub warfare would be like? As subs on the Soviet side got quieter wouldn’t that require US subs to get in closer to passively detect them? Would a submarine know for sure that a super cav weapon fired back their way response to their torpedo would miss?
 
As subs on the Soviet side got quieter wouldn’t that require US subs to get in closer to passively detect them?
Not necessarily, with modern submarines your primary means of detection will be narrowband--they simply don't emit much broadband energy. These detection ranges can vary wildly.

Would a submarine know for sure that a super cav weapon fired back their way response to their torpedo would miss?
Almost certainly. First, you're going to fire from an advantageous position that an adversary can't immediately counterfire upon, and anything they fire upon is going to be a place you're no longer at.

Regarding supercavitating weapons, they effectively go in a straight line. Sonar systems simply don't have the vertical beamwidth to resolve depression/elevation accurately enough to reliably hit a submerged contact. A 30 foot tall target at 1000 yds requires an accuracy of half a degree.

I believe a Mk 48 is currently going for $5mil each. That’s not cheap or simple sounding.
Yeah, they aren't cheap. Despite what some may say, this isn't WW2--the primary mission of any SSN is to destroy other submarines, we're not gonna waste our time and resources plinking at hapless skimmers. To do this job, you need a weapon that is reliable 100% of the time, and a Mk48 is as close as you're feasibly going to get.
 
Would this apply to ANY underwater launched ASWweapon?
There's always angular uncertainty in sonar and beams get wider as frequencies get lower. This is before you even consider depression/elevation uncertainty caused by sound speed changes. It's why we use guided weapons.

How much worse is torpedo guidance on its own without the wire?
As long as your initial solution was half-decent it really doesn't need the host platform anymore. Hell the weapon is likely smarter than the operator sitting at BYG.
 
Yeah, they aren't cheap. Despite what some may say, this isn't WW2--the primary mission of any SSN is to destroy other submarines, we're not gonna waste our time and resources plinking at hapless skimmers. To do this job, you need a weapon that is reliable 100% of the time, and a Mk48 is as close as you're feasibly going to get.
Of all the post WW2 weapons that have been developed and used and to whatever extent judged one way or another, the ASW sub and to a lesser extent surface/air launched torpedo is the one with an almost non existent track record.

Hundreds (thousands?) of AAMs have been fired in anger and there’s a track record.
Thousands of SAMs launched and there’s a track record.
ATGMs same.
Even AShMs have some use.

Sub launched ASW torpedoes fired in anger is 1? Side question is did the San Luis find a British SSN??! That’s probably unlikely.

Modern surface/air launched ASW torp firings in combat are the 50 or so ones the British launched in the Falklands. End result was probably whalers cursing their primitive methods.
https://www.usni.org/magazines/proceedings/1984/march/where-were-those-argentine-subs
Can a single Mk 48 or a Spearfish take down a Rooskie SSN or SSGN/BN? I don’t think the stand-off distance provided by their outer hulls is going to stop a very big hole being blown into the pressure hull by a TNT equivalent 1200lb shaped charge. But will it be big enough of a hole to put it on the bottom? Can more than 1 torp be guided to one target?
 
Can a single Mk 48 or a Spearfish take down a Rooskie SSN or SSGN/BN?
Yeah, one torpedo is going to disable any submarine. Whatever the weapon doesn't destroy, the water will, and no amount of damage control is stopping it.

Can more than 1 torp be guided to one target?
Yeah, absolutely, but there's generally little reason to.
 
I don't think those have the discharge rate that AgZn or Li do. So they have great range but bad speed. Good for recon UUVs, bad for torpedoes.

The current push for electric vehicles is driving advances in battery technology, so we should see more progress in that area. This should also be good news for conventionally-powered submarines:

"Solid-state batteries store more energy in a smaller and lighter package, offering two to 10 times the capacity of lithium-ion batteries and providing quicker charging capabilities. They eliminate the flammable liquid electrolyte used in commercial lithium-ion batteries and are considered safer."

See:

https://eepower.com/news/beyond-li-ion-5-top-battery-tech-advances-in-2024/
 
Note that that article is 41 years old and from the Sub League newsletter--they'll publish articles from any rando scrub so don't assume there's much due diligence or genuine expert commentary in them. Some of the assertions in that article are pretty silly.

Torpedoes have grown quieter over the decades but there is no torpedo on Earth that you could genuinely consider "quiet" at full speed. They run at very high RPMs and they really aren't large enough for the extensive isolation you'll find on submarines. It isn't really a problem though, because torpedo seekers are highly directional and aren't really susceptible to self-noise.

There was an earlier effort to quiet the Mark 48, but it didn't go anywhere:

Navy Torpedo Programs: MK-48 ADCAP Upgrades Not Adequately Justified (Letter Report, 06/12/95, GAO/NSIAD-95-104):

https://www.globalsecurity.org/military//library/report/gao/gao95104.htm
https://www.gao.gov/assets/nsiad-92-191.pdf

But the Mark 48, Mod 6, ended up incorporating some degree of noise reduction:

"The TPU upgrade significantly reduced the torpedo’s noise signature making it substantially quieter (one of the main criticisms of previous mods)."

See:

https://thetidesofhistory.com/2024/07/21/advanced-capabilities-u-s-mark-48-torpedo/
 
There was an earlier effort to quiet the Mark 48, but it didn't go anywhere:
I kept coming across this criticism of the noise levels of the 48. Would be interesting to compare it with noise levels of the Mk 48 Mod 0 (the turbine version that wasn’t picked)/Spearfish (which used an upgraded version of that turbine engine).
 
What I’ve read is that the main concern about the Mk 48 especially in arctic warfare which because of the sound conditions would require getting in real close, firing a 48 would be the submarine pulling its pants down and giving away its location. They didn’t know about it then but that’s where the Soviet rocket torpedo may have ended up with 1:1 kill ratios.
What you'd detect is the impulse pump firing. That's (relatively) loud, even on an Ohio with a turbine impulse pump.

Then you hear the engine and screws light off.

Sonar is calling Torpedo in the Water based on the impulse pump firing, not the torpedo lighting off. They're calling your outbound unit based on hearing the engine light off.



Isn’t that what arctic sub warfare would be like? As subs on the Soviet side got quieter wouldn’t that require US subs to get in closer to passively detect them? Would a submarine know for sure that a super cav weapon fired back their way response to their torpedo would miss?
But the ranges you'd be looking at for taking that shot, usually from in someone's baffles, are more like the outer edge of the range of OG Shkval.



How far off target can a sub go b4 it breaks the wire?
You can maneuver some, but not a whole lot. About as much as you can with your towed arrays out, so it's not that big a deal
 
Then you get to spend a couple minutes at an awkward down bubble to slide the tube-end of the wire spool out of the tubes before you can reload the tube.

So the guide-wire spool isn't ejected from the torpedo-tube after it has been cut?
 
Spearfish Mod.1 officially entered service this year after validation live firing on all classes. It entered development in 2009 with a target of first entering production in 2019. Entered production in 2020 with first live firings in Feb 2021.

Main change is an insensitive warhead, changing the guidance wire to fibre optic, computer upgrade, and change of fuel from a combination of Otto II with HAP oxidiser to running on pure Otto II.
 
There have been some rumors that they might switch the next iteration of Mk 48 (or successor) to electric rather than the swashplate IC motor in the current version. High energy density batteries like lithium ion are becoming a credible alternative to Otto fuel.

The FY 2026 request for budget authorization for the mk48 states a supposed switch to the stored chemical energy propulsion for the mod 9.
1762760098057.png
https://www.highergov.com/budget/mk-48-adcap-f4adcde/

Now whether its going to be a similar SF6/Li Rankine engine as the mk50 (or L3Harris's mk54 mod 2), or some other exotic combo, its anyone's guess.
 
But the ranges you'd be looking at for taking that shot, usually from in someone's baffles, are more like the outer edge of the range of OG Shkval.
1989 USN sub wouldn’t know that. Maybe on the inside submariners know differently but from what I’ve read and it’s fairly extensive on the outside under ice combat would involve getting real close and getting shot back at almost as quickly as you shot first.
 

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