Poland's edge: Tube artillery outshines American might
The US Army is significantly stronger than the Polish Army, though there is one aspect where Poland holds an undisputed advantage over the Americans. We reveal the secret of Polish tube artillery as compared to the American counterpart.
The Polish Army is currently updating its Soviet-era artillery systems, such as the 2S1 Gvozdika and the wz. 1977 DANA, many of which have been sent to Ukraine. They are replacing these with K9 Thunder and AHS Krab self-propelled howitzers in NATO-standard 155 mm calibre. These systems are world-class with guns measuring 52 calibres in length (8 metres), which allow for target engagements up to 80 kilometres with suitable ammunition.
By comparison, the core of the US Army's tube artillery comprises the M109A7 Paladin howitzers, which are extensive modernisations of the M109 howitzers introduced in the 1960s. As part of the M109A7 Paladin upgrade, older models, starting from the M109A5, received enhancements in armour, engine and suspension, increased ammunition and crew safety, and howitzer digitisation.
However, the 155 mm gun with a length of 39 calibres (6 metres) was not altered, which significantly limits the range compared to modern competitors. The range limitation is approximately 30 kilometres for the rocket-assisted M549A1 shells or 40 kilometres for the M982 Excalibur shells.
The US Army resorts to imports
The delay in artillery upgrades in the US Army is a result of budgetary policy and the reorientation of the armed forces towards expeditionary operations after the fall of the USSR, where heavily armoured self-propelled artillery was thought unnecessary.
The first consequence was the cancellation in 1992 of the Armored Systems Modernization (ASM) programme, which had been in progress since the 1980s. It was intended to introduce a new family of heavy vehicles for the US Army, including a successor to the M109.
However, in 1994, a separate project for the American howitzer of the future continued under the XM2001 Crusader programme. This aimed 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. Intriguingly, the required rate of fire was achieved through automatic loading and water cooling of the gun, akin to the naval 76/62 Super Rapido (SR).
Additionally, the completed prototype was expected to be capable of starting bombardment within 15-30 seconds and offering the capability to fire up to eight rounds in MRSI (multiple round simultaneous impact) mode. The programme, valued at the time at 11 billion dollars, was burdensome for the budget, and it was further hindered by the opinion of the GAO, the American equivalent of the Supreme Audit Office, in 1996. It suggested terminating the programme and purchasing the German PzH 2000 howitzer or modernising existing M109 howitzers.
The Americans, as usual, opted for the patriotic route, similar to the M14 rifles, and chose to modernise the M109 howitzers to the M109A7 Paladin standard. This led to the cancellation of the XM2001 Crusader programme in 2002.
This left the US Army with short-range artillery and necessitated another programme with the codename XM1299 ERCA (Extended Range Cannon Artillery), initiated in 2019 to improve the situation. It involved mounting a prototype 58 calibre (9 metres) gun by BAE Systems in the M109 howitzer. The tests showed some success, but the ERCA programme was cancelled in 2024.
The reason was the excessively rapid wear of components (barrel or breech), which deviated too much from the intervals adopted by the US Army. This means the United States' only chance for modern artillery is the import of a ready foreign solution under the programme SPH-M (Self-Propelled Howitzer Modernization).
Participants include the following companies: 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 version of K9 Thunder and RCH 155 seem to be favourites.
Range in tube artillery — a longer barrel is essential
Artillery shells are accelerated by gases produced by the combustion of the propellant charge, much like firearms. Generally, 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 m/s, whereas for a shell fired under identical conditions from a 52 calibre barrel, it was already 945 m/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 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 increasing the range without using various "tricks," which have their drawbacks. When using the simplest DM121 shells with the shorter gun, the range is 24 kilometres, while for the longer one, it is 31/32 kilometres. On the other hand, employing a base-bleed unit in the shell's base, generating exhaust gases that reduce drag, allows for a 30% range increase, with longer guns gaining more.
Similarly, the situation is with shells equipped with a rocket engine, which further increases the shell's velocity after leaving the barrel. The engine works for a few seconds and then burns out. This results in a range of over 50 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 possess 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 substitute for a short gun, and if the USA wants to catch up with the rest of the NATO countries, they must embark on an expensive overhaul of tube artillery to incorporate new systems.
