Poland's artillery prowess: Why US lags in range
The US Army is significantly stronger than the Polish Army, but there is one aspect in which Poland holds an undisputed advantage over the Americans. We explain the secret of Polish tube artillery compared to the American one.
The Polish Army is currently in the process of replacing Soviet-era artillery systems like the 2S1 Gvozdika, many of which have been sent to Ukraine, along with the wz. 1977 DANA, with K9 Thunder and AHS Krab self-propelled howitzers in NATO-standard 155 mm caliber. These are world-class systems with guns measuring 52 calibers in length (26 feet) that offer target engagements at distances of up to 50 miles with the appropriate ammunition.
In comparison, the core of the US Army's tube artillery consists of the M109A7 Paladin howitzers, which are comprehensive modernizations of the M109 howitzers introduced into service in the 1960s. As part of the upgrade to the M109A7 Paladin standard, older versions starting from the M109A5 received improvements in armor, engine and suspension, increased safety for transported ammunition and crew, and digitization of the howitzer.
However, the 155 mm gun with a length of 39 calibers (20 feet) was not changed, which considerably limits the range compared to modern competitors. The range is essentially limited to 19 miles for the rocket-assisted M549A1 shells or 25 miles for the M982 Excalibur shells.
The US Army resorts to imports
The delay in artillery upgrades in the US Army is the result of budgetary policy and a reorientation of the armed forces towards expeditionary operations after the fall of the USSR, where heavily armored self-propelled artillery was deemed unnecessary.
The first consequence of this issue was the cancellation in 1992 of the Armored Systems Modernization (ASM) program, which had been underway since the 1980s. It was intended to introduce a new family of heavy vehicles for the US Army, including a successor to the M109.
In 1994, a separate project for the future American howitzer continued under the XM2001 Crusader program. This was designed to develop a howitzer based on the M1 Abrams tank chassis with a range of over 25 miles and a firing rate of 10 rounds per minute. Interestingly, the required rate of fire was achieved through the implementation of automatic loading and water cooling of the gun, similar to the naval 76/62 Super Rapido (SR).
Additionally, the completed prototype was supposed to be capable of starting bombardment within 15-30 seconds and offered the ability to fire up to eight rounds in MRSI (multiple round simultaneous impact) mode. The program, valued at the time at 11 billion dollars, proved burdensome for the budget, and it was further hindered by a 1996 opinion from the GAO, the American equivalent of the Supreme Audit Office. It suggested ending the program and purchasing the German PzH 2000 howitzer or modernizing existing M109 howitzers.
The Americans, following their usual preference, opted to modernize the M109 howitzers to the M109A7 Paladin standard, rather than importing. This decision led to the cancellation of the XM2001 Crusader program in 2002.
This left the US Army with short-range artillery and spurred another program with the codename XM1299 ERCA (Extended Range Cannon Artillery), which was started in 2019 to improve the situation. It involved mounting a prototype 58 caliber (30 feet) gun by BAE Systems in the M109 howitzer. While the tests showed some successes, the ERCA program was canceled in 2024.
The reason was the excessively fast wear of components (barrel or breech), which deviated too much from the intervals adopted by the US Army. This means the only chance for modern artillery in the US Army may be the import of a ready foreign solution under the program SPH-M (Self-Propelled Howitzer Modernization).
Participants include companies like American Rheinmetall Vehicles with the RCH 155 howitzer, BAE Bofors (H77BW Archer), Hanwha Defense USA (K9 Thunder), the KNDS and General Dynamics Land Systems alliance (HX3 with AGM module), and Elbit Systems USA (ATMOS 2000). The results are not yet known, but the latest versions of K9 Thunder and RCH 155 seem to be favorites.
Range in tube artillery — a longer barrel is essential
Artillery shells are accelerated by gases produced by the combustion of the propellant charge, similar to firearms. Generally speaking, the longer they are accelerated, the faster they become. For example, in one of Rheinmetall’s propellant charge tests, the L15A1 shell fired from a 39 caliber barrel at an air temperature of 70°F had a muzzle velocity of 2,657 ft/s, whereas for a shell fired under identical conditions from a 52 caliber barrel, it was already 3,100 ft/s.
The difference also lies in a larger breech, which accommodates more propellant charge to ensure identical pressure as in the shorter barrel. For 155 mm barrels with a length of 39 calibers, the standard is a chamber with a capacity of 4.9 gallons, while for those 52 calibers long, it is 6.1 gallons. Manufacturers usually state the maximum pressure for shells to be around 58,000 psi.
This all allows for increasing the range without resorting to various "tricks," which have their drawbacks. For example, using the simplest DM121 shells for the shorter gun limits the range to 15 miles, while for the longer one, it is 19/20 miles. On the other hand, using a base-bleed unit in the shell's base, which generates exhaust gases that reduce drag, allows for a 30% range increase, with the longer guns gaining more.
A similar situation occurs with shells featuring a rocket engine, which further increases the shell's velocity after it leaves the barrel. The engine works for a few seconds and then burns out. This translates to a range of over 31 miles for longer guns but at the cost of reducing the amount of TNT in the shell, as room needs to be made for the engine and rocket fuel. Typically, it is over 11 lbs compared to 20/22 lbs for regular shells.
Another option is the use of sub-caliber shells, which are smaller than the bore diameter and encased in a sabot that falls away after firing. These sub-caliber shells have a better ballistic coefficient than traditional ones, losing energy more slowly. An example is the guided Vulcano GLR shells with a range of 43-50 miles for longer guns or 31-34 miles for shorter ones.
Nothing can replace a short gun, and if the US wants to catch up with the rest of the NATO countries, it must undertake an expensive overhaul of its tube artillery to adopt new systems.
