Bad ideas in war

[theprestige]

As far as I can tell, railguns seem to be in search of a niche between close range and cruise missile/mrbm range. The obvious advantages are:

1. A smaller, faster projectile that is harder to track, target and intercept; and
2. A much higher ammo capacity, meaning longer/more engagements before needing to retire and reload.

It seems like the applications should be other surface combatants that have been detected at long range, and land targets where shore defenses are either weak or nonexistent. In principle, it should be a lot cheaper to park a battlecruiser off the coast of Yemen, and rail Houthi positions ashore, instead of expending cruise missiles on them.

It also makes it safer to bombard important Chinese coastal facilities. The gun can be fired from much further away than current naval guns. It carries a lot more ammunition than can fit into missile magazines. And the platform itself is much harder to pick up on radar. Similar advantages are apparent for target rich environments such as a Chinese amphibious assault on Taiwan, where you'd have a lot of stuff worth shooting. China is also likely to have very heavy air defenses, which would tend to reduce the value of a carrier-based bombardment strategy.

That said, railguns kind of look like one of those highly desirable techs, like fusion power, that will always be just around the corner. It's obvious that the US isn't there yet.

The "better than nothing" alternative gun, the one with the really expensive ammunition, is the real problem child, in my opinion. It's basically just a bigger naval gun, with smarter shells. Ground-launched glide bombs, basically. While I think "smartillery" is the way of the future, I'm not sure a bigger naval gun is the quantum leap forward in capability we're looking for. I suspect we're better off continuing to make incremental improvements in carrier-based bombardment, supplemented by missiles, until we hit upon the Next Big Thing.

 

[Andy_Ross]

The Royal Navy was considering Battleships with 20" guns before the Washington Treaty and British manufacturing had the capability.
Making bigger conventional guns isn't hard.

 

[Jack by the hedge]

Recoil isn't the same as conventional artillery. The main forces are not opposite the direction of the projectile but at 90 degrees and try to push the rails apart.
At the present time a set of rails is only good for a few shots before heat, stress and friction degrade them to a point where they need to be replaced.

While I haven't thought about the internal forces trying to pull a rail gun to pieces, I'm very sure the total momentum of the gun and projectile will be conserved, so the gun will be hurled backwards as forcefully as the projectile is hurled forwards.

 

[theprestige]

The Royal Navy was considering Battleships with 20" guns before the Washington Treaty and British manufacturing had the capability.
Making bigger conventional guns isn't hard.

Nobody said it was hard. But bigger conventional guns really don't seem to be the meta, at the moment. The trend in surface combat seems to be towards smaller guns with smarter shells, leaving more room for larger gun magazines and/or more room for missiles.

 

[Andy_Ross]

While I haven't thought about the internal forces trying to pull a rail gun to pieces, I'm very sure the total momentum of the gun and projectile will be conserved, so the gun will be hurled backwards as forcefully as the projectile is hurled forwards.

No, that's the point, some of it is directed at right angles to the length of the rail.

 

[Andy_Ross]

Nobody said it was hard. But bigger conventional guns really don't seem to be the meta, at the moment. The trend in surface combat seems to be towards smaller guns with smarter shells, leaving more room for larger gun magazines and/or more room for missiles.

I agree, the point of battleship guns was to penetrate the armour of other battleships.

 

[jimbob]

While I haven't thought about the internal forces trying to pull a rail gun to pieces, I'm very sure the total momentum of the gun and projectile will be conserved, so the gun will be hurled backwards as forcefully as the projectile is hurled forwards.

Andy is correct about the magnetic repulsive forces trying to push the rails apart - which again would lead to the requirement for a bulkier gun and indeed the life is a problem. I agree that railguns don't seem to be practical yet, but all the features would suggest that they would make most sense in large warships

The Royal Navy was considering Battleships with 20" guns before the Washington Treaty and British manufacturing had the capability.
Making bigger conventional guns isn't hard.

But you are still limited to probably under Mach 3 with a gun powered by conventional explosives. Maybe you can get more with some fancy explosives technology but controlling those is probably harder than electrical switching for a linear motor in a railgun.

As far as I can tell, railguns seem to be in search of a niche between close range and cruise missile/mrbm range. The obvious advantages are:

1. A smaller, faster projectile that is harder to track, target and intercept; and
2. A much higher ammo capacity, meaning longer/more engagements before needing to retire and reload.

It seems like the applications should be other surface combatants that have been detected at long range, and land targets where shore defenses are either weak or nonexistent. In principle, it should be a lot cheaper to park a battlecruiser off the coast of Yemen, and rail Houthi positions ashore, instead of expending cruise missiles on them.

It also makes it safer to bombard important Chinese coastal facilities. The gun can be fired from much further away than current naval guns. It carries a lot more ammunition than can fit into missile magazines. And the platform itself is much harder to pick up on radar. Similar advantages are apparent for target rich environments such as a Chinese amphibious assault on Taiwan, where you'd have a lot of stuff worth shooting. China is also likely to have very heavy air defenses, which would tend to reduce the value of a carrier-based bombardment strategy.

That said, railguns kind of look like one of those highly desirable techs, like fusion power, that will always be just around the corner. It's obvious that the US isn't there yet.

The "better than nothing" alternative gun, the one with the really expensive ammunition, is the real problem child, in my opinion. It's basically just a bigger naval gun, with smarter shells. Ground-launched glide bombs, basically. While I think "smartillery" is the way of the future, I'm not sure a bigger naval gun is the quantum leap forward in capability we're looking for. I suspect we're better off continuing to make incremental improvements in carrier-based bombardment, supplemented by missiles, until we hit upon the Next Big Thing.

Agree with pretty much all of this, except possibly the utility against moving surface targets at long range, where I suspect they wouldn't be that useful compared to missiles.

 

[jimbob]

No, that's the point, some of it is directed at right angles to the length of the rail.

Yes but that is in addition to the recoil of the shell. The rails pushing each other apart don't actually add to the recoil as such as each rail is its partner's recoil mass

 

[jimbob]

Recoil isn't the same as conventional artillery. The main forces are not opposite the direction of the projectile but at 90 degrees and try to push the rails apart.
At the present time a set of rails is only good for a few shots before heat, stress and friction degrade them to a point where they need to be replaced.

Of course the AGS of the Zumwalt got round any concerns about barrel life by having the number of shells as the limiting factor.

 

[theprestige]

Of course the AGS of the Zumwalt got round any concerns about barrel life by having the number of shells as the limiting factor.

The AGS was not a railgun. It was the "better than nothing" conventional naval gun they wanted to adopt after they realized the railgun tech wasn't ready yet. The number of shells was limited because the AGS was a much larger caliber than existing naval guns, meaning larger shells and therefore fewer shells per magazine.

Also, because the Z class never went into service, neither did the AGS. This meant that they couldn't leverage economies of scale in the production of these high-advanced smart shells. This in turn meant that the price per shell for the prototypes was extremely high. This led to the canard that the shells were an obscenely expensive waste of money. It's the same thing with the F-35 being cheaper per unit than the F-22. It's not tha that the F-22 was overpriced, it's that we ended up not making very many of them - for very good reasons.

 

[catsmate]

Also there's the question of recoil. A 50kg shell launched at 2.5km/second is far easier to handle in a turret massing several hundred tonnes in a ship of several thousand tonnes compared to a vehicle massing several tens of tonnes, whilst rockets and missiles can have almost* no recoil.

I'm guessing friction could end up giving a small analogue of recoil in the direction of launch as opposed to against it

Well yess, sort-of. The acceleration cycle of an emag launcher is less 'jerky' (in the sense of fourth order derivative) than a conventional CPR launcher so the stresses of recoil are less, and the 'barrel' of an emag weapon doesn't have to be as structurally strong as one containing a violent deflagration.
Current 155mm weapons can launch a 45kg at >900m/s.

Wrt rockets (and ramjets) burning propellent outside of the containment of a barrel is far less efficient.

 

[catsmate]

plenty of time to acquire by a ship and for it to take evasive action.
Also as the projectile is not powered it will be losing velocity as soon as it leaves the gun.

And, as recent events have shown, you don't need to destroy a missile or projectile to render it ineffective, just deflect it slightly.

 

[catsmate]

The Royal Navy was considering Battleships with 20" guns before the Washington Treaty and British manufacturing had the capability.
Making bigger conventional guns isn't hard.

Logistics!!
Improving 155mm (and 203mm) shells is probably a better route.

 

[catsmate]

I'd also like to point out that the Swedes are already pushing 155mm ramjet test shells to well over 100km with plans for 150km. Perhaps the US Navy should (again) ask the Swedes for assistance?
Or (worse) ask the US Army, who's working with Nammo, to help....

 

[theprestige]

I'd also like to point out that the Swedes are already pushing 155mm ramjet test shells to well over 100km with plans for 150km. Perhaps the US Navy should (again) ask the Swedes for assistance?
Or (worse) ask the US Army, who's working with Nammo, to help....

Why? The USN already has domestic contractors working on the same things.

 

[jimbob]

Well yess, sort-of. The acceleration cycle of an emag launcher is less 'jerky' (in the sense of fourth order derivative) than a conventional CPR launcher so the stresses of recoil are less,

d⁴x/dt⁴?

I sort of assumed a deflagration would give a rapid change in acceleration but I guess it wouldn't be linear.

Whereas one could easily time the current through every section of a railgun.

 

[jimbob]

The AGS was not a railgun. It was the "better than nothing" conventional naval gun they wanted to adopt after they realized the railgun tech wasn't ready yet. The number of shells was limited because the AGS was a much larger caliber than existing naval guns, meaning larger shells and therefore fewer shells per magazine.

Also, because the Z class never went into service, neither did the AGS. This meant that they couldn't leverage economies of scale in the production of these high-advanced smart shells. This in turn meant that the price per shell for the prototypes was extremely high. This led to the canard that the shells were an obscenely expensive waste of money. It's the same thing with the F-35 being cheaper per unit than the F-22. It's not tha that the F-22 was overpriced, it's that we ended up not making very many of them - for very good reasons.

Yes, we're violently agreeing, I think.

My point is that the F22 had a role in a way that the Zumwalt didn't (even if I think the YF23 looked more potentially impressive and maybe closer to what the 6th generation fighters seem to be shaping up to)

 

[jimbob]

This video suggests that the Japanese idea of having magnesium* "thermite" shells for any guns equivalent to a destroyer's main armament and up might have been a bit of a mistake.


TLDW, starting very hot fires that can't** be extinguished by water or CO2


*Not sure if it is a thermite reaction or just magnesium in there, hence the quotation marks.


** I guess that water could still cool it and work that way, but a lot of hydrogen and oxygen would still be produced in that case.

 

[catsmate]

d⁴x/dt⁴?

I sort of assumed a deflagration would give a rapid change in acceleration but I guess it wouldn't be linear.

Whereas one could easily time the current through every section of a railgun.

Exactly. And you can do fancy stuff with spin, especially with a projectile with the ability to change trajectory.

 

[catsmate]

This video suggests that the Japanese idea of having magnesium* "thermite" shells for any guns equivalent to a destroyer's main armament and up might have been a bit of a mistake.


TLDW, starting very hot fires that can't** be extinguished by water or CO2


*Not sure if it is a thermite reaction or just magnesium in there, hence the quotation marks.


** I guess that water could still cool it and work that way, but a lot of hydrogen and oxygen would still be produced in that case.

It's not true 'thermite', i.e. the Goldschmidt reaction, but barium nitrate and magnesium, plus some rubber. The Tirpitz also used such shells.
They were generally ineffective.