[GK3]

It makes me wonder who makes the best self propelled 155?

It certainly isn't the United States. The consensus is that the South Korean K9 Thunder is the best thing going. This is partially because it is affordable, but all in all it is a very good system. It must also be said that many of the export sales of this system include options (like fire control systems) that are customer specific. Thus the K9 isn't exactly one product. It does however use the German technology for extra range as reverse engineered by the Koreans. As of now, the K9A2 is the best thing going.

It must be said that the US Army is of at least two minds regarding the future of artillery. The Army has spent and wasted many billions of dollars trying to figure out how it would project force in the future. Lost was spent trying to develop a liquid propellant artillery piece that would have ranges greater than the RAP rounds of the current 155 mm howitzers. They couldn't make it work. https://www.gao.gov/products/nsiad-95-25 https://en.wikipedia.org/wiki/XM2001_Crusader.

As the above links demonstrate, part of the problem was that the civilian leadership was  focused on a lighter, more mobile force to combat terrorism and rouge states, not near-peer opponents. Another part of the problem is that the Army did not, and does not, know what it wants (if anything) in a self-propelled howitzer (SPH). Most important, given the role of the USAF and its capabilities to provide support, it is arguable that SPH are simply obsolete. Coupled with Army owned long range missiles the ability to bring massive precision fires upon any point of the battlefield in the matter of a few minutes arguably reduces the survivability of artillery to zero. It has been consensus for quite a few years that towed artillery was unsurvivable.

The argument for the SPH is that it can fire and move quickly to avoid the LRASMs and PrSMs that will rain down upon them. One problem with this approach is that while these SPH are moving, they aren't firing. Another is that logistically supporting these SPH when nobody know how many times they will have to move and to where is virtually impossible. The reasons the users are searching for SPH that have longer range is that first they can be further back from the FEBA. This makes counter-battery from the shorter range enemy SPH ineffective. Second, it allows SPHs spead over a wider geographic area to attack any given point. This mitigates the requirement to move fairly frequently because other units can take up the slack. The obvious problem in the first case is that the enemy is also increasing his range in the same manner. The second case requires communication and coordination among geographically (and organizationally) dispersed  units. That isn't easy.

Most importantly, aircraft, large drones, and ballistic missiles will always outrange artillery. It is just physics. The "boost phase" of an artillery projectile must take place while the projectile is in the barrel (RAP excepted). If one wants to increase range one must increase the barrel length and/or diameter. More propellant can then be used, but any that doesn't burn while the projectile is still in the barrel is wasted. There are obvious limitations on size, weight, and breech pressure that limit gunnery range. What can reasonably be done has been done.  These facts limit the "specific impulse" that can be applied because it has to occur very quickly. A rocket engine can burn "for a long time". Aircraft and drones can operate their engines for hours.

SPH main historical advantages were 1) they could respond quicker and in larger volume that missiles, drones, or aircraft, and 2) they could provide large volumes of fire over long periods of time (persistence of fire). Of course if they aren't survivable, it doesn't matter. The US Army doesn't know what it thinks about this, so here we sit.

It should also be noted that the Advanced Gun System (AGS) for the Zumwalt destroyers was a failure. The eventual cost of the projectiles was prohibitive, in the $800,000 to $1,000,000 per shell. That got the program cancelled. I am guessing that was partially a political excuse. It is almost certain the whole concept was fatally flawed from day 1 and never actually "worked".

Ukraine seems to be proving that small cheap drones even without fancy guidance systems can function as counter battery fire.  Ukraine has cost russia billions I would think just via their cheap drone systems.  How many drones can you build for the cost of a SPH?  Do you think Reaper drones can survive very long in peer vs peer conflicts?  They were great when the other side had no real airdefense systems, but I wonder how long one would survive in the Ukraine vs Russia conflict. I presume we are working on smaller, much cheaper drones with at least semi hardened controls etc.  The Ukraine conflict is sort like either the Spanish Civil War or WWI when new technology came on line and changed the nature of conflicts.

[GK3]

It makes me wonder who makes the best self propelled 155?

It certainly isn't the United States. The consensus is that the South Korean K9 Thunder is the best thing going. This is partially because it is affordable, but all in all it is a very good system. It must also be said that many of the export sales of this system include options (like fire control systems) that are customer specific. Thus the K9 isn't exactly one product. It does however use the German technology for extra range as reverse engineered by the Koreans. As of now, the K9A2 is the best thing going.

It must be said that the US Army is of at least two minds regarding the future of artillery. The Army has spent and wasted many billions of dollars trying to figure out how it would project force in the future. Lost was spent trying to develop a liquid propellant artillery piece that would have ranges greater than the RAP rounds of the current 155 mm howitzers. They couldn't make it work. https://www.gao.gov/products/nsiad-95-25 https://en.wikipedia.org/wiki/XM2001_Crusader.

As the above links demonstrate, part of the problem was that the civilian leadership was  focused on a lighter, more mobile force to combat terrorism and rouge states, not near-peer opponents. Another part of the problem is that the Army did not, and does not, know what it wants (if anything) in a self-propelled howitzer (SPH). Most important, given the role of the USAF and its capabilities to provide support, it is arguable that SPH are simply obsolete. Coupled with Army owned long range missiles the ability to bring massive precision fires upon any point of the battlefield in the matter of a few minutes arguably reduces the survivability of artillery to zero. It has been consensus for quite a few years that towed artillery was unsurvivable.

The argument for the SPH is that it can fire and move quickly to avoid the LRASMs and PrSMs that will rain down upon them. One problem with this approach is that while these SPH are moving, they aren't firing. Another is that logistically supporting these SPH when nobody know how many times they will have to move and to where is virtually impossible. The reasons the users are searching for SPH that have longer range is that first they can be further back from the FEBA. This makes counter-battery from the shorter range enemy SPH ineffective. Second, it allows SPHs spead over a wider geographic area to attack any given point. This mitigates the requirement to move fairly frequently because other units can take up the slack. The obvious problem in the first case is that the enemy is also increasing his range in the same manner. The second case requires communication and coordination among geographically (and organizationally) dispersed  units. That isn't easy.

Most importantly, aircraft, large drones, and ballistic missiles will always outrange artillery. It is just physics. The "boost phase" of an artillery projectile must take place while the projectile is in the barrel (RAP excepted). If one wants to increase range one must increase the barrel length and/or diameter. More propellant can then be used, but any that doesn't burn while the projectile is still in the barrel is wasted. There are obvious limitations on size, weight, and breech pressure that limit gunnery range. What can reasonably be done has been done.  These facts limit the "specific impulse" that can be applied because it has to occur very quickly. A rocket engine can burn "for a long time". Aircraft and drones can operate their engines for hours.

SPH main historical advantages were 1) they could respond quicker and in larger volume that missiles, drones, or aircraft, and 2) they could provide large volumes of fire over long periods of time (persistence of fire). Of course if they aren't survivable, it doesn't matter. The US Army doesn't know what it thinks about this, so here we sit.

It should also be noted that the Advanced Gun System (AGS) for the Zumwalt destroyers was a failure. The eventual cost of the projectiles was prohibitive, in the $800,000 to $1,000,000 per shell. That got the program cancelled. I am guessing that was partially a political excuse. It is almost certain the whole concept was fatally flawed from day 1 and never actually "worked".

Ukraine seems to be proving that small cheap drones even without fancy guidance systems can function as counter battery fire.  Ukraine has cost russia billions I would think just via their cheap drone systems.  How many drones can you build for the cost of a SPH?  Do you think Reaper drones can survive very long in peer vs peer conflicts?  They were great when the other side had no real airdefense systems, but I wonder how long one would survive in the Ukraine vs Russia conflict. I presume we are working on smaller, much cheaper drones with at least semi hardened controls etc.  The Ukraine conflict is sort like either the Spanish Civil War or WWI when new technology came on line and changed the nature of conflicts.