Polish artillery outpaces outdated US systems in range battle

Currently, the Polish Army is in the process of replacing Soviet-era artillery systems like the 2S1 Gvozdika, many of which have been sent to Ukraine, and the wz. 1977 DANA with K9 Thunder and AHS Krab self-propelled howitzers in the NATO-standard 155 mm calibre. These are world-class systems with guns measuring 52 calibres in length (8 metres), allowing engagements at distances of up to 80 kilometres with the appropriate ammunition.

In comparison, the core of the US Army’s tube artillery consists of the M109A7 Paladin howitzers, which are extensive modernizations of the M109 howitzers introduced in the 1960s. As part of the upgrade to the M109A7 Paladin standard, older versions starting from the M109A5 received improvements in armour, engine with suspension, increased safety for stored ammunition and crew, and digitization of the howitzer.

However, the 155 mm gun with a length of 39 calibres (6 metres) was not changed, which considerably limits its range compared to more modern competitors. The maximum range is essentially 30 kilometres for the rocket-assisted M549A1 shells or 40 kilometres for the M982 Excalibur shells.

The delay in upgrading artillery within the US Army is the result of budgetary policy and a reorientation of the armed forces towards expeditionary operations following the fall of the USSR, where heavily armoured self-propelled artillery was seen as unnecessary.

The first outcome of this issue was the cancellation in 1992 of the Armored Systems Modernization (ASM) program, which had been in progress since the 1980s. It was intended to introduce a whole new family of heavy vehicles for the US Army, including a successor to the M109.

However, in 1994, a separate project for the future American howitzer continued under the XM2001 Crusader program. This was intended to develop a howitzer based on the M1 Abrams tank chassis with a range of over 40 kilometres 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 for the gun, similar to the naval 76/62 Super Rapido (SR).

Additionally, the completed prototype was supposed to be capable of initiating bombardment within 15-30 seconds and offer the ability to fire up to eight rounds in MRSI (multiple round simultaneous impact) mode. The program, valued at 11 billion dollars at the time, was heavy on the budget, and 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, as always, chose the patriotic route, just like with the M14 rifles, and decided to modernize the M109 howitzers to the M109A7 Paladin standard. This led to the cancellation of the XM2001 Crusader program in 2002.

This left the US Army with short-range artillery and another program with the codename XM1299 ERCA (Extended Range Cannon Artillery), initiated in 2019 to resolve the issue. The project involved mounting a prototype 58 calibre (9 metres) gun by BAE Systems in the M109 howitzer. The tests saw some successes, but the ERCA program was cancelled in 2024.

The reason was excessively fast wear of components (barrel or breech), which deviated too much from the intervals accepted by the US Army. This means the only opportunity for modern artillery for the US Army may be the import of a ready foreign solution under the program SPH-M (Self-Propelled Howitzer Modernization).

Participants include companies such as 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 the favourites.

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 instance, in one of Rheinmetall’s propellant charge tests, the L15A1 shell fired from a 39 calibre barrel at an air temperature of 21°C had a muzzle velocity of 810 metres per second, whereas for a shell fired under identical conditions from a 52 calibre barrel, it reached 945 metres per second.

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 calibres, the standard is a chamber with a capacity of 18.5 litres, while for those 52 calibres long, it is 23 litres. Manufacturers usually state the maximum pressure for shells is around 4,000 bar.

This allows for an increased range without using various "tricks," which have their drawbacks. When using ordinary DM121 shells for the shorter gun, the range is 24 kilometres, while for the longer one, it is 30/32 kilometres. On the other hand, using a base-bleed unit in the shell's base generating exhaust gases that reduce drag allows for a 30% range increase, with the longer guns gaining more.

The situation is the same with shells equipped with 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 results in a range of over 51 kilometres 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 5 kilograms compared to 9/10 kilograms for regular shells.

Another option is the use of sub-calibre shells, which are smaller than the bore diameter and encased in a sabot that falls away after firing. These sub-calibre 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 69-80 kilometres for longer guns or 50-55 kilometres for shorter ones.

Nothing can replace a short gun, and if the USA wants to catch up with the rest of NATO countries, they must undertake an expensive overhaul of tube artillery to new systems.