Editing M109 howitzer (section)

==Variants<span class="anchor" id="types"></span>==

=== M109 ===
First produced in 1963. It had a 155&nbsp;mm M126 cannon in an M127 mount, and carried 28 rounds of 155&nbsp;mm ammunition. It was also armed with a .50cal [[M2 Browning machine gun|M2HB]] machine gun with 500 rounds of ammunition. Easily identified by its short barrel and a double baffle [[muzzle brake]] with a large fume extractor just behind it. Maximum range of 14,600 meters.

==== M109G ====
[[File:M109 der Bundeswehr.jpg|left|thumb|M109G of the [[Bundeswehr]] in 1982]]
The [[West German]] army M109s were designated as the M109G, and featured a [[breechblock]] system developed by Rheinmetall extending the effective range to {{convert|18|km|mi}} or {{convert|18.5|km|mi}} according to some sources, a new fire control system, and three smoke dischargers mounted on either side of the turret as well.{{sfn|Foss|1979|page=358}}{{sfn|Foss|2011|page=868}}

In December 1966, the United States and Norway signed an agreement related to the co-production of the M109G.<ref>{{Cite book |title=Treaties in Force: A List of Treaties and Other International Agreements of the United States in Force on January 1, 1986 |publisher=United States Department of State |year=1986 |page =135}}</ref>

=== M109A1 ===
[[File:United States Army M109A1 self-propelled howitzer in Germany during exercise REFORGER '82.jpg|thumb|US Army M109A1 in 1982|left]]
Fielded in 1973, this modification replaced the M126 cannon with a 39 caliber M185, featuring a longer barrel while increasing maximum range to 18,100 meters.<ref name=":0">{{Cite journal |date=October 1989 |title=Numbering the M109 Howitzers |url=https://books.google.com/books?id=Hgh5tz5WsQoC&pg=PA52 |journal=Field Artillery |publisher=US Field Artillery Association |pages=52 |issn=0899-2525}}</ref>

==== M109A1B ====
The M109 rebuilt to M109A1 standard.

==== M109 66/74 ====
{{Main|M109 in the Swiss Armed Forces}}
The M109 (Pz Hb) 66/74 is a Swiss upgraded M109 (Pz Hb 66) to M109A1B (Pz Hb 74) standard.

Switzerland purchased 146 M109 under the armament program 1968, and introduction of the howitzer started in 1971.<ref name="Pz Hb 66">{{Cite web |title= Panzerhaubitze 66 M-109 / L-2315,5 cm Pz Hb 66 - Panzerhaubitzen - Raupenfahrzeuge {{!}} militärfahrzeuge.ch |url=https://militaerfahrzeuge.ch/unterkategorie_13_31_355.html |access-date=2023-07-28 |website=militaerfahrzeuge.ch}}</ref> All vehicles received upgrade to M109A1B (Pz Hb 74) standard and were delivered from May 1977 to February 1979.<ref name="Pz Hb 66/74">{{Cite web |title=Panzerhaubitze 66/74 M-109 / L-39Pz Hb 66/74 - Panzerhaubitzen - Raupenfahrzeuge  |url=https://militaerfahrzeuge.ch/unterkategorie_13_31_475.html |access-date=2023-07-28 |website= Militaerfahrzeuge}}</ref>

=== M109A2 ===
Incorporated 27 [[Reliability, availability, maintainability and safety|Reliability, Availability, and Maintainability (RAM)]] mid-life improvements. Most notably, the long barreled 155&nbsp;mm M185 Cannon in the new M178 gun mount, ballistic protection for the panoramic telescope, counterbalanced travel lock, and the ability to mount the M140 bore sight alignment device. Stowage of 155 mm rounds increased from 28 to 36 rounds; .50cal ammunition remained at 500 rounds. Fielded in 1979.<ref name=":0" />

During M109A2 production, a slightly simplified version was also produced for export. This had minor internal changes and deleted the hull flotation feature. These were designated '''M109A1B'''.<ref>{{cite book |last1=Lathrop|first1=R.|title=M109 155mm Self-Propelled Howitzer 1960–2005|date=5 Feb 2005|publisher=Osprey |isbn=978-1-84176631-7|page=15}}</ref>

==== K55 ====
[[File:2013.3. 해병대 자주포 기동훈련 Rep.of Korea Marine Corps Self-propelled artillery Maneuvers (8553361055).jpg|left|thumb|K-55 howitzers of [[Republic of Korea Marine Corps]] in 2013]]
The K55 is a South Korean license produced variant of the M109A2. In the 1960s, the [[Republic of Korea Army|South Korean Army]] received [[M107 self-propelled gun|M107]] and [[M110 howitzer|M110]] from the United States. However, the number of these self-propelled guns was insufficient to counter rapidly-growing North Korean artillery capabilities. In the 1970s, South Korea began mass-producing towed howitzers locally, but intelligence reports of North Korean [[M-1978 Koksan|170 mm self-propelled artillery]] forced South Korea to look for a new self-propelled artillery system.<ref name="K55 interview" />

In December 1983, the ministers of defense of the United States and South Korea signed a [[memorandum of understanding]] (MOU) to co-produce M109A2 in South Korea using American technical data. The United States delivered two completed M109A2s to South Korea for operational review, and the [[Agency for Defense Development]] began to translate the data package and created field and maintenance manuals for soldiers. South Korea wanted to produce every part of the vehicle domestically; however, due to the amendment bill by Rep. [[Samuel S. Stratton]] of New York, which established a limit for foreign military technology cooperation, the turret and the M185 cannon from [[Watervliet Arsenal]] were imported from the United States.<ref name="K55 interview"/>

Compared to the M109A2, besides 63 percent of parts being produced locally, K55 has a driver's night periscope and light exposure minimization device to enhance night-time operations as well as additional radio systems. The vehicle has a [[CBRN defense|nuclear, biological and chemical]] protection system and halon fire extinguishers. A total of 1,180 K55s were produced between 1985 and 1996.<ref name="K55 interview"/><ref name="K66">{{Cite web |title=[김대영의 무기 인사이드] 우리 군에서 영구 결번된 비운의 국산장갑차 'K66' |url=https://nownews.seoul.co.kr/news/newsView.php?id=20210316601008 |access-date=2022-08-08 |website=나우뉴스 | date=16 March 2021 |language=ko}}</ref> The vehicle's name was changed from KM109A2 to K55, originally a code name from the Samsung factory.

In November 1990, the United States and South Korea signed an agreement to allow South Korea to supply M109 parts to third parties.<ref>{{Cite web |last=李敦琯|title=한반도 전쟁발발시 美전투력 즉각 증강 |url=https://n.news.naver.com/mnews/article/001/0003458242?sid=102 |access-date=2022-08-08 |website=[[Naver News]] |language=ko}}</ref> In May 1997, during the Security Cooperation Committee held in Washington D.C., South Korea requested that the United States revise the MOU to export complete K55s, originally intended for domestic use only. South Korea was expecting to export 72 K55s and four ammunition support vehicles to Brazil for $160 million over Belgium's offer, but the [[United States Department of Defense]] declined the request to avoid an arms race in the region.<ref>{{Cite web |title=국산 1백55mm 자주포 대량수출 전망 |url=https://n.news.naver.com/mnews/article/001/0004226305?sid=102 |access-date=2022-08-08 |website=[[Naver News]] |language=ko}}</ref><ref>{{Cite web |title=1백55mm 국산자주포 수출 무산 |url=https://n.news.naver.com/mnews/article/001/0004248291?sid=102 |access-date=2022-08-08 |website=[[Naver News]] |language=ko}}</ref>

In May 1998, the South Korean military began operating a K55 simulator to boost artillery operator training. The simulator took a year and a billion [[South Korean won|KRW]] budget to develop. It is expected to save 150 million KRW per year per device.<ref>{{Cite web |last=朴成雨|title=포병학교 자주포 조종 시뮬레이터 개발 |url=https://n.news.naver.com/mnews/article/001/0004367835?sid=102 |access-date=2022-08-08 |website=[[Naver News]] |language=ko}}</ref>

=== M109A3 ===
M109A1s rebuilt to M109A2 standard, also fielded in 1979.<ref name=":0" /> Some A3s feature three contact arm assemblies{{Explain|date=January 2023}}, while all A2s have five.

==== M109A3B ====
M109A1B rebuilt to M109A2 standard.

==== M109A3G ====
In 1983, the [[German Army]] purchased 586 conversion kits from the FMS Corporation (now Marvin Land Systems) to convert its fleet of M109Gs to the M109A3G standard. This upgraded variant uses a new gun barrel developed by Rheinmetall, giving an extended range of {{convert|24|km|mi}}. It also features a new fire-control system, and three forward firing 76&nbsp;mm smoke grenade launchers on either side of the turret.{{sfn|Foss|2011|page=868}}

==== M109A3GN ====
[[File:UA 72nd bde M109A3GN 04.jpg|thumb|Ukraine's [[72nd Mechanized Brigade (Ukraine)|72nd Mechanized Brigade]] operating an M109A3GN during the [[Russian invasion of Ukraine]]]]
Between 1969 and 1971 Norway acquired 126 M109Gs from West Germany.{{citation needed|reason=This statement contradicts with the U.S. official documents, reference is at M109G regarding co-production. |date=December 2023}} They were then upgraded to the M109A3GN configuration during the latter half of the 1980s.<ref name="M109A3GNM">{{cite web|url=https://www.forsvaret.no/aktuelt-og-presse/aktuelt/feature/denne-gjor-haeren-sterkere|title=Denne gjør Hæren sterkere|language=no|work=[[Norwegian Armed Forces|Forsvaret]]|date=2020-09-04|access-date=2022-06-04}}</ref>

==== M109L ====

=== M109A4 ===
Soon after the adoption of A2/A3 versions, the Division Weapon Support System study was initiated in 1980, which by the end of the decade resulted in the development of several modernization packages.<ref name=":0" /> The most modest one was the Howitzer Extended Life Program update originally designated as M1903A3E1<ref name=":1">{{Cite journal |last=Fogle |first=Charles J. |date=July–August 1986 |title=Howitzer Modernization Program Comparisons |url=https://books.google.com/books?id=l6QrAAAAYAAJ&pg=RA3-PA26 |journal=Field Artillery |publisher=US Field Artillery Association |pages=26}}</ref> and later adopted as M109A4, initially scheduled for 1985-1987<ref>{{Cite book |last=Defense |first=United States Congress House Committee on Appropriations Subcommittee on Department of |url=https://books.google.com/books?id=3oi2AAAAIAAJ&pg=RA3-PA329 |title=Department of Defense appropriations for 1984: hearings before a subcommittee of the Committee on Appropriations, House of Representatives, Ninety-eighth Congress, first session |date=1983 |publisher=U.S. Government Printing Office |language=en}}</ref> but actually fielded in 1989 in the [[United States Army Reserve|Reserve Component of the US Army]].<ref name=":0" />

This modernization program fitted M109A2s and M109A3s with Nuclear, Biological, and Chemical / Reliability, Availability, and Maintainability (NBC/RAM) improvements, including air purifiers, heaters, and [[MOPP (protective gear)|Mission Oriented Protective Posture (MOPP) (protective)]] gear.

The traversing mechanism's clutch was changed to be hydraulic (as compared to the electric mechanism on previous M109s), and added a manual override. The M109A4 also gained a second hydraulic filter and more reliable engine starting equipment which greatly improved the ability to start the vehicle in an emergency.

Ammunition stowage remained the same as in previous models.

=== M109A5 ===
[[File:Egyptian M109 self-propelled howitzer being decontaminated during Operation Desert Shield.JPEG|right|thumb|An Egyptian M109A5 being decontaminated during [[Operation Desert Shield]].]]

This modification was also designed for the US Army Reserve, originally planned as an update for all M109A4s under the second phase of the Reserve Component Modified Armament System to bring the range up to the version adopted as M109A6.<ref name=":0" /><ref>{{Cite book |last=Office |first=United States General Accounting |url=https://books.google.com/books?id=Sk8sAAAAIAAJ&pg=PA24 |title=Army's M109 Howitzer: Required Testing Should be Completed Before Full-rate Production : Report to the Secretary of Defense |date=1992 |publisher=The Office |language=en}}</ref> It was fielded in 1991 in much smaller numbers than originally devised<ref>{{Cite book |last=Pierrot |first=Lane |url=https://books.google.com/books?id=gCkzXGSh_70C&pg=PA51 |title=The Long-term Implications of Current Defense Plans |date=2003 |publisher=Congress of the United States, Congressional Budget Office |isbn=978-0-16-051268-1 |language=en}}</ref> due to the [[Cold War (1985–1991)|end of the Cold War]].

It replaced the 155&nbsp;mm M185 cannon in an M178 mount with a 39-caliber 155&nbsp;mm M284 cannon in an M182 mount developed for the M109A3E2 (see below), giving the A5 a maximum range of 22,000 meters with unassisted projectiles and 30,000 meters with [[rocket-assisted projectile]] (RAP) rounds.<ref>{{Cite web |url=http://fas.org/man/dod-101/sys/land/m109.htm |title=M109 155mm SP Howitzer |access-date=9 May 2016 |archive-url=https://web.archive.org/web/20160507184707/http://fas.org/man/dod-101/sys/land/m109.htm |archive-date=7 May 2016 |url-status=live }}</ref> The vehicle can carry 36 complete rounds of ammunition and has a 440&nbsp;hp engine instead of the standard 405&nbsp;hp engine.

==== M109A5+ ====
Various manufacturers have upgraded the fire control and other components of the M109A5. BAE Systems in [[York, PA]] recently delivered 12 M109A5+ vehicles to Chile and 32 M109A5+ vehicles for Brazil.

=== M109A6 Paladin ===
[[File:M-109A6 Paladin firing.jpg|right|thumb|A M109A6 "Paladin" firing at night]]
[[File:Fallujah11092004-11-09.jpg|right|thumb|An M109A6 firing a shell during combat operations in Fallujah, Iraq]]

Also originating in the Division Weapon Support System study in early 1980s, the Howitzer Improvement Program was devised as a more extensive modernization than the Howitzer Extended Life Program. The vehicle was originally designed as M109A3E2 before being adopted as M109A6<ref name=":0" /> and is now better known as Paladin (M109A3E3 was to feature a longer barrel<ref name=":1" /> but was not adopted). 

The Paladin model has improvements in the areas of survivability, RAM, and armament. This includes increased armor, a redesigned internal arrangement for safer ammunition and equipment storage, engine and suspension upgrades, and improvement of the M284 Cannon and M182A1 Mount. The greatest difference is the integration of an inertial navigation system, sensors detecting the weapons' lay, automation, and an encrypted digital communication system, which utilizes computer controlled frequency-hopping to avoid enemy [[electronic warfare]] and allow the howitzer to send grid location and altitude to the battery [[fire direction center|Fire Direction Center (FDC)]]. 

The battery FDCs coordinates fire through a battalion or higher FDC. This allows the Paladin to halt from the move and fire within 30 seconds, with an accuracy equivalent to the previous models when properly emplaced, laid, and safed—a process that previously required several minutes under the best of circumstances. Tactically, this improves the system's survivability by allowing the battery to operate dispersed in pairs across the countryside, and allowing the howitzer to quickly move between salvos, or if attacked by indirect fire, aircraft, or ground forces.

Ammunition storage of 155&nbsp;mm rounds was increased from 36 to 39.

Developed from 1984, it was adopted in 1990 with original plans to field the weapon in 1991<ref name=":0" /> later slipping to 1992<ref>{{Cite book |url=https://books.google.com/books?id=3ShMsInluuEC&pg=RA1-PA42 |title=Army RD & A. |date=1991 |publisher=Office for the Deputy Director, Acquisition Career Management |language=en}}</ref> and finally to 1993.<ref>{{Cite book |url=https://books.google.com/books?id=CagrAAAAYAAJ&pg=PA155 |title=Weapon Systems |publisher=Department of the Army, Office of the Deputy Chief of Staff for Research, Development, and Acquisition |language=en}}</ref> The US Army received the last of 950 Paladins it had ordered in June 1999.<ref name=":3">{{Cite web |last=Carter |first=Rakeem |date=2022-06-06 |title=Raiders kick off modernization process |url=https://www.army.mil/article/257286/raiders_kick_off_modernization_process#:~:text=It%20is%20also%20the%20year,and%20campaigns%20across%20the%20globe. |access-date=2025-01-25 |website=www.army.mil |language=en}}</ref> Seven further Paladins were ordered for the National Guard in July 2000, with an additional eighteen received in January 2002.<ref name=":4">{{Cite web |title=Paladin M109A6 155mm Artillery System |url=https://www.army-technology.com/projects/paladin/ |access-date=2025-01-25 |website=Army Technology |language=en-US}}</ref> In May 2022, the US Army began shipping its M109A6 Paladins for refitting to the M109A7 standard in order to begin the process of modernization.<ref name=":3" />

=== M109 KAWEST ===
{{See also|M109 in the Swiss Armed Forces}}[[File:M109kawest.JPG|thumb|A Swiss M109 KAWEST howitzer in 2009]]
This Swiss improved version produced by [[RUAG]] incorporates a new Swiss-designed L47 155&nbsp;mm gun with an increased firing range of up to 36&nbsp;km. It features an [[inertial navigation system]] coupled with a new gun-laying system, along with an ammunition storage increase of 40 rounds and 64 charges. The KAWEST (lit. ''Kampfwertsteigerung'' = upgrade of combat capabilities) requires only six crew members instead of eight. It is able to fire three-round bursts within 15 seconds, or maintain a constant firing rate of over one round per minute.<ref name = 'RUAG'>{{cite web|title = M109|website = ruag.com|url = https://www.ruag.com/en/products-services/land/vehicles-weapon-systems/indirect-fire-artillery/m109|access-date = 9 May 2018|archive-url = https://web.archive.org/web/20180709193055/https://www.ruag.com/en/products-services/land/vehicles-weapon-systems/indirect-fire-artillery/m109|archive-date = 9 July 2018|url-status = live}}</ref><ref name = 'Chile'>{{cite web|title = Chile Requests a Mechanized Artillery Battalion|website = Defense Industry Daily|url = https://www.defenseindustrydaily.com/Chile-Requests-a-Mechanized-Artillery-Battalion-05515/|date = 6 October 2011|access-date = 9 May 2018|archive-url = https://web.archive.org/web/20180509220622/https://www.defenseindustrydaily.com/Chile-Requests-a-Mechanized-Artillery-Battalion-05515/|archive-date = 9 May 2018|url-status = live}}</ref>

Upgraded Swiss PzHb (Panzerhaubitze)74, 79 and 88 (M109A1B) are known as respectively '''PzHb 74/95'',''''' '''PzHb 79/95''' and '''PzHb 88/95'''.<ref>{{Cite web |title=Panzerhaubitze 74/95, 79/95, 88/95 M-109A1B / L-47, 15,5 cm Pz Hb KAWEST L47 - Panzerhaubitzen - Kettenfahrzeuge {{!}} militärfahrzeuge.ch |url=https://militaerfahrzeuge.ch/unterkategorie_13_31_478.html |access-date=2023-01-29 |website=militaerfahrzeuge.ch}}</ref>

* 33 of the 120 PzHb 74 were modernised to the standard PzHb 74/95 KAWEST.<ref name=":9">{{Cite web |title=Panzerhaubitze 74 M-109A1B/ L-39Pz Hb 74 M-109 - Panzerhaubitzen - Raupenfahrzeuge {{!}} militärfahrzeuge.ch |url=https://militaerfahrzeuge.ch/unterkategorie_13_31_356.html |access-date=2023-07-28 |website=militaerfahrzeuge.ch}}</ref>
* 207 of the 207 PzHb 79 were modernised to the standard PzHb 79/95 KAWEST.<ref name=":10">{{Cite web |title=Panzerhaubitze 79 M-109A1B / L-39Pz Hb 79 M-109 - Panzerhaubitzen - Raupenfahrzeuge {{!}} militärfahrzeuge.ch |url=https://militaerfahrzeuge.ch/unterkategorie_13_31_357.html |access-date=2023-07-28 |website=militaerfahrzeuge.ch}}</ref> 
* 108 of the 108 PzHb 88 were modernised to the standard PzHb 88/95 KAWEST.<ref>{{Cite web |title=Panzerhaubitze 74/95, 79/95, 88/95 M-109A1B / L-47, 15,5 cm Pz Hb KAWEST L47 - Panzerhaubitzen - Raupenfahrzeuge {{!}} militärfahrzeuge.ch |url=https://militaerfahrzeuge.ch/unterkategorie_13_31_478.html |access-date=2023-07-28 |website=militaerfahrzeuge.ch}}</ref>

=== M109A3GNM ===
The latest version in service with the Norwegian Army's [[Artillery Battalion (Norway)|Artilleribataljonen]]. 

In 2006, there were 56 M109A3GNs in the Army's inventory, meaning that at least 70 SPGs had been scrapped after the end of the Cold War. 14 of the M109A3GNs received upgrades in 2007, and were designated M109A3GNM. The upgrade includes a new intercom and new navigation and positioning systems.<ref name="M109A3GNM" />

In 2020 the 14 units with A3GNM upgrades and those still with A3GN specs were placed in storage because all the new Korean [[K9 Thunder]] units had been delivered.<ref name="M109A3GNM"/> In May 2022, Norway donated 22 A3GN-spec M109s to Ukraine.<ref name=donation>{{cite web|url=https://www.regjeringen.no/en/aktuelt/norge-har-donert-artilleriskyts-til-ukraina/id2917760/|title=Norway has donated M109 to Ukraine|website=regjeringen.no (Norwegian Government)|date=8 June 2022}}</ref> Two M109A3GN howitzers were destroyed and three damaged during the [[2022 Russian invasion of Ukraine]].<ref>{{Cite web |last=Oryx |title=Attack On Europe: Documenting Ukrainian Equipment Losses During The 2022 Russian Invasion Of Ukraine |url=https://www.oryxspioenkop.com/2022/02/attack-on-europe-documenting-ukrainian.html |access-date=2022-11-05 |website=Oryx}}</ref>

=== M109 KAWEST WE ===
Improvement of the Swiss Kawest variant, 133 in total were brought up to this standard:

* 25 of the 207 PzHb 79/95 were modernised to the standard PzHb KAWEST WE.<ref name=":112">{{Cite web |title=Panzerhaubitze M-109A1B KAWEST WEPz Hb M-109 KAWEST WE - Panzerhaubitzen - Raupenfahrzeuge {{!}} militärfahrzeuge.ch |url=https://militaerfahrzeuge.ch/unterkategorie_13_31_724.html |access-date=2023-07-28 |website=militaerfahrzeuge.ch}}</ref> Those are currently in service.
* 108 of the 108 PzHb 88/95 were modernised to the standard PzHb KAWEST WE.<ref name=":112"/> Those are currently in service.

=== K55A1 ===
[[File:2013.1.2 육군 1군단 K-55A1 포병사격 Rep.of Korea Army K-55A1 (8340099583).jpg|thumb|K55A1 howitzers firing on an exercise in 2013]]
The K55A1 is a South Korean overhaul and modernization of the K55, augmenting the proven systems of the [[K9 Thunder]] and the K9A1. The development took three years between 2007 and 2010. The upgrade started in 2010.<ref name="K55 interview"/> In November 2010, in the wake of the [[Bombardment of Yeonpyeong|North Korean artillery attack]], the South Korean government authorized a massive increase in military spending. South Korea allocated 11.5 billion KRW on K55A1 upgrades for FY2011, more than a 1500% increase from 700 million KRW for FY2010.<ref>{{Cite web |last=김 |first=남권 |title=국방위, 내년 국방예산 7천146억원 증액 의결 |url=https://n.news.naver.com/mnews/article/001/0004795198?sid=100 |access-date=2022-08-12 |website=[[Naver News]] |language=ko}}</ref> The upgrade was performed by Samsung Techwin, and the first vehicle was fielded by the South Korean Army in early 2011.<ref>{{Cite web  |title=K55A1 자주포 |url=https://kookbang.dema.mil.kr/newsWeb/m/20181211/1/BBSMSTR_000000100036/view.do |access-date=2022-08-10 |website=국방일보 |archive-date=7 April 2023 |archive-url=https://web.archive.org/web/20230407115918/https://kookbang.dema.mil.kr/newsWeb/20181211/1/BBSMSTR_000000100036/view.do |language= ko |url-status=live }}</ref>

The K55A1 is fitted with the same electronics and fire control system as the K9. The self-propelled gun has significantly enhanced field operability and accuracy through the installation of [[Honeywell Aerospace]]'s TALIN 5000 INS (inertial navigation system), a satellite navigation device (GPS), and a speed calibrator. As a result, the vehicle automatically lays the gun in the desired direction and delivers a first round within 45 seconds between stops, or 75 seconds between maneuvers after receiving the shooting specification, which required 2 minutes and 11 minutes, respectively, on the K55.<ref name="K55 interview"/><ref name="K55A1">{{Cite web  |title=생존·기동·효율성 완벽 호흡…'환상의 짝꿍' 자랑 |url=https://kookbang.dema.mil.kr/newsWeb/m/20210803/1/BBSMSTR_000000100115/view.do |access-date=2022-08-14 |website=국방일보 |archive-date=7 April 2023 |archive-url=https://web.archive.org/web/20230407115922/https://kookbang.dema.mil.kr/newsWeb/20210803/1/BBSMSTR_000000100115/view.do |language = ko |url-status=live }}</ref><ref name="youtube_MITm4IWHwpo">{{Citation |title=똑똑하게 다시 태어났다 K55A1 자주포 | date=20 January 2021 |url=https://www.youtube.com/watch?v=MITm4IWHwpo |language=en |access-date=2022-08-12}}</ref>

With the help of a new semi-autoloader, while charges are still inserted manually, the howitzer can fire 4 rounds per minute, increased from 2 to 3 rounds per minute. The improved suspension, involving a strut-type hydropneumatic buffer from Mottrol Co, Ltd., along with an enhanced chamber, allowed the vehicle to shoot K307 and K310 ammunition designed for K9 platform without laying spades at a maximum distance of 32&nbsp;km. An APU (auxiliary power unit) was installed to operate the howitzer without turning on the main engine.<ref name="K55 interview"/><ref name="K55A1"/><ref name="youtube_MITm4IWHwpo"/>

The Army Consolidated Maintenance Depot joined the K55A1 upgrade, releasing its first results in December 2013.<ref>{{Cite web  |title=전투장비 100% 성능발휘 보장 |url=https://kookbang.dema.mil.kr/newsWeb/m/20131224/2/BBSMSTR_000000010023/view.do |access-date=2022-08-10 |website=국방일보 |archive-date=7 April 2023 |archive-url=https://web.archive.org/web/20230407115918/https://kookbang.dema.mil.kr/newsWeb/20131224/2/BBSMSTR_000000010023/view.do| language= ko|url-status=live }}</ref> The upgrade cost 20% of the K9 Thunder, 800 million KRW, as of 2021.<ref name="K55A1"/> The K55A1 upgrade program was completed in December 2022.<ref>{{Citation |title=K-9만큼 똑똑해진 K55A1 업그레이드! (feat. K56) 리얼웨폰172 | date=3 January 2023 |url=https://www.youtube.com/watch?v=INi6I8Jx99o |access-date=2023-05-28 |language=ko}}</ref>

=== M109A7 ===
<gallery mode="packed" heights="180">
File:Bae PIM upgrade.jpg|A prototype M109A7
File:M109A7_Self-propelled_Howitzer.jpg|A M109A7 155 mm SPH being tested at Yuma Proving Ground, Arizona
</gallery>

The newest M109 version for U.S. service is the M109A7, formerly known as the M109A6 Paladin Integrated Management (PIM). The M109A7 shares common chassis components with the [[Bradley Fighting Vehicle|Bradley Fighting Vehicle (BFV)]] such as the engine, transmission, and tracks. This creates commonality with other systems and maximizes cost savings in production, parts inventory, and maintenance personnel. The M109A7's onboard power systems harness technologies originally developed for the [[XM1203 non-line-of-sight cannon]].<ref name="Kris Osborn"/>

The electric drive is faster than the previous hydraulic system, and the automatic rammer more consistently rams the round into the gun for consistent velocities and better accuracy. It features a 600-volt onboard power system to accommodate additional armor and future networking technologies as they become ready. The M109A7 can sustain a one-round per-minute rate of fire and a maximum rate of fire of four rounds per minute.<ref name="Kris Osborn"/> Weighing {{convert|78,000|lb|kg|abbr=on}}, the M109A7 is {{convert|10,000|lb|kg|abbr=on}} heavier than its predecessor, and it has the capacity to grow to {{convert|110,000|lb|kg|abbr=on}}. Even with the weight increase, the M109A7 can travel faster than previous versions at {{convert|38|mph|km/h|abbr=on}} and is more maneuverable than a BFV.<ref>[http://webarchive.loc.gov/all/20140427212218/http://www.defensenews.com/article/20140427/DEFREG02/304270019/US%2DArmy%2DBreaking%2DOut%2DBig%2DNew%2DGuns US Army Breaking Out the Big New Guns] – Defensenews.com, 27 April 2014</ref>

Prototypes of the vehicle underwent government testing in preparation for a [[Low rate initial production|Low-Rate Initial Production (LRIP)]] decision. The testing included RAM, mission and ballistic hull and turret testing. The M109A7 was slated to begin LRIP by 2013. The U.S. Army planned on procuring a fleet of 580 sets of M109A7 howitzers and [[M992 field artillery ammunition supply vehicle|M992A3 field artillery ammunition supply vehicles]].<ref name="Kris Osborn">{{cite web|url=https://www.army.mil/article/64728/Army_developing_new_self_propelled_howitzer/|title=Army developing new self-propelled howitzer|date=1 September 2011|access-date=5 September 2011|archive-url=https://web.archive.org/web/20121011131704/http://www.army.mil/article/64728/Army_developing_new_self_propelled_howitzer/|archive-date=11 October 2012|url-status=live}}</ref>

In October 2013, the [[Defense Acquisition Board]] approved the decision to start M109A7 production. The FY 2014 budget called for $340.8 million in Paladin funding, which would be two dozen vehicle sets at $14.4 million per vehicle. The Army plans to buy 133 vehicles, in 66 one-half vehicle sets starting in 2014. One M109A7 howitzer and two supporting M992A3 ammunition carriers will be destroyed during tests. A Full-Rate Production (FRP) decision was planned for February 2017.<ref>[http://www.armyrecognition.com/october_2013_defense_industry_military_news_uk/bae_systems_could_obtain_contract_u.s._army_for_m109a6_pim_155m_self-propelled_howitzer_2610134.html BAE Systems could obtain new contract from U.S. Army for M109A7 155m self-propelled howitzer] {{Webarchive|url=https://web.archive.org/web/20131029030258/http://www.armyrecognition.com/october_2013_defense_industry_military_news_uk/bae_systems_could_obtain_contract_u.s._army_for_m109a6_pim_155m_self-propelled_howitzer_2610134.html |date=29 October 2013 }} – Armyrecognition.com, 26 October 2013</ref><ref>[https://archive.today/20131026162811/http://www.defensenews.com/article/20131021/SHOWSCOUT04/310210031/New-Paladin-Enter-Low-Rate-Production New Paladin to Enter Low-Rate Production] – Defensenews.com, 21 October 2013</ref> 

In October 2013, BAE received a $668 million contract to begin LRIP of the M109A7.<ref>[http://www.baesystems.com/article/BAES_162972/bae-systems-awarded-contract-to-begin-production-of-paladin-integrated-management?_afrLoop=38999698147000 BAE Systems Awarded Contract to Begin Production of Paladin Integrated Management] {{Webarchive|url=https://web.archive.org/web/20131102100557/http://www.baesystems.com/article/BAES_162972/bae-systems-awarded-contract-to-begin-production-of-paladin-integrated-management?_afrLoop=38999698147000 |date=2 November 2013 }} – BAE press release, 31 October 2013</ref> The first M109A6 and M992A2 vehicles were rebuilt to M109A7 and M992A3 standards as part of LRIP beginning in summer 2014.<ref>[http://www.armyrecognition.com/may_2014_global_defense_security_news_uk/self-propelled_howitzer_m109a7_and_m992a3_carrier_ammunition_enter_in_service_with_u.s._army_2005141.html Self-propelled howitzer M109A7 and M992A3 carrier ammunition enter in service with U.S. Army] {{Webarchive|url=https://web.archive.org/web/20150716133646/http://www.armyrecognition.com/may_2014_global_defense_security_news_uk/self-propelled_howitzer_m109a7_and_m992a3_carrier_ammunition_enter_in_service_with_u.s._army_2005141.html |date=16 July 2015 }} – Armyrecognition.com, 20 May 2014</ref> LRIP deliveries began in April 2015.<ref>[https://www.army.mil/article/146200/Army_accepts_delivery_of_first_M109A7_Self_Propelled_Howitzer_system/ Army accepts delivery of first M109A7 Self-Propelled Howitzer system]  – Army.mil, 9 April 2015</ref> The contract for FRP was signed in December 2017, with 48 vehicles slated for construction.<ref>{{cite web|url=http://mil-embedded.com/news/u-s-army-contracts-for-full-rate-production-on-m109a7-weapon-vehicle/|title=U.S. Army contracts for full-rate production on M109A7 weapon vehicle – Military Embedded Systems|website=mil-embedded.com|access-date=28 December 2017|archive-url=https://web.archive.org/web/20171227213426/http://mil-embedded.com/news/u-s-army-contracts-for-full-rate-production-on-m109a7-weapon-vehicle/|archive-date=27 December 2017|url-status=live}}</ref> The Army plans to upgrade 689 Paladins to A7-standard.<ref>[https://www.armytimes.com/news/your-army/2019/03/22/plan-would-double-artillery-upgrades-in-army-arsenal-over-the-next-five-years/ Plan would double artillery upgrades in Army arsenal over the next five years]. ''Army Times''. 22 March 2019.</ref>

[[File:XM1113 in flight.jpg|thumb|A XM1113 extended range artillery round, shown here at a range demonstration, uses a rocket-assist motor]]
The Army is looking to increase the capabilities of the M109A7. By introducing the new XM1113 [[Rocket-Assisted Projectile|Rocket-Assisted Projectile (RAP)]],<ref name=judson20180320 /> it can reach {{cvt|40|km|abbr=on}} from the current 39-caliber barrel. An additional XM1113 improvement over the legacy RAP round is the replacement of the high explosive, TNT, with an insensitive munition that is less volatile and less prone to unplanned detonation.<ref>{{Cite web |last=Eshel |first=Tamir |date=2016-10-14 |title=US Army to Deploy Safer, Extended Range Rocket-Assisted Artillery Round - Defense Update |url=https://defense-update.com/20161014_xm1113.html |access-date=2025-01-01 |language=en-US}}</ref> The Army is working on an autoloader to increase the sustained rate of fire to 6–10 rounds per minute.<ref name=judson20180320 >[https://www.defensenews.com/land/2018/03/20/army-to-demonstrate-precision-strike-hypersonics-and-ramjet-capabilities-in-just-a-few-years/ US Army to demo precision strike, hypersonics, ramjet capabilities in just a few years]. ''Defense News''. 20 March 2018.</ref>{{needs update|date=March 2025}}

Another part of the effort is the use of a new supercharged propellant to fire the shells, which required redesigning the howitzer to handle higher pressures.<ref>[https://breakingdefense.com/2020/03/new-army-cannon-doubles-range/ New Army Cannon Doubles Range; Ramjet Ammo May Be Next]. ''Breaking Defense''. 6 March 2020.</ref>{{needs update|date=March 2025}}

==== Hypervelocity projectile (HVP) ====
In January 2016, the U.S. Army test-fired hypervelocity projectiles originally designed for use by [[U.S. Navy]] [[electromagnetic railgun]]s. They found that they significantly increased the gun's range. The Army is looking into using the M109 Paladin firing the HVP for [[ballistic missile defense]], as traditional missile interceptors are expensive, and gun-based missile defense used for point defense would use artillery at a much lower cost per round.<ref>[http://www.defenseone.com/technology/2016/02/New-weapons-pentagon-wants-tomorrows-wars/125611/  These Are the New Weapons the Pentagon Chief Wants for Tomorrow’s Wars] {{Webarchive|url= https://web.archive.org/web/20160203091722/http://www.defenseone.com/technology/2016/02/New-weapons-pentagon-wants-tomorrows-wars/125611/ |date=3 February 2016}}, Defense one, 2 February 2016</ref><ref>[http://www.military.com/daily-news/2016/02/02/micro-drones-arsenal-plane-railguns-funded-new-defense-budget.html  'Micro' Drones, 'Arsenal' Plane, Railguns Funded in New Defense Budget] {{Webarchive|url= https://web.archive.org/web/20161008083056/http://www.military.com/daily-news/2016/02/02/micro-drones-arsenal-plane-railguns-funded-new-defense-budget.html |date= 8 October 201}}, Military.com, 2 February 2016.</ref>  

The HVP is capable of being fired out to {{convert|50|nmi|mi km}} from a conventional cannon. It weighs {{convert|68|lb|kg|abbr=on}} with a {{convert |46|lb|kg|abbr=on}} flight body containing its guidance and warhead—less powerful, but more agile to hit small, high-speed targets. Modifications will be needed for the Paladin to effectively shoot the HVP, possibly including different propellant to achieve higher velocities, automated reloading systems to fire quickly enough to defeat salvo launches, improved barrel life, and a new fire control and sensor system.<ref>[http://breakingdefense.com/2016/02/carters-strategic-capabilities-office-arsenal-plane-missile-defense-gun/ Robot Boats, Smart Guns & Super B-52s: Carter’s Strategic Capabilities Office] {{Webarchive |url= https://web.archive.org/web/20160209230845/http://breakingdefense.com/2016/02/carters-strategic-capabilities-office-arsenal-plane-missile-defense-gun/ |date=9 February 2016}}, ''Breaking defense'', 5 February 2016</ref> During a test of the Air Force's Advanced Battle Management System (ABMS) in September 2020, an HVP fired from an Army Paladin howitzer successfully intercepted a [[Composite Engineering BQM-167 Skeeter|BQM-167]] target drone simulating a [[cruise missile]].<ref>[https://breakingdefense.com/2020/09/abms-demo-proves-ai-chops-for-c2/ ABMS Demo Proves AI Chops For C2]. ''Breaking Defense''. 3 September 2020.</ref><ref>[https://www.airforcemag.com/smart-bullet-downs-cruise-missile-in-2nd-abms-test/ ‘Smart’ Bullet Downs Cruise Missile in 2nd ABMS Test]. ''Air Force Magazine''. 4 September 2020.</ref>

HVP was renamed to gun-launched guided projectile (GLGP),<ref>{{cite news |url=https://news.usni.org/2023/04/27/report-to-congress-on-navy-shipboard-lasers-4 |title= Report to Congress on Navy Shipboard Lasers |last1=O'Rourke |first1=Ronald |date=21 April 2023 |website= USNI |publisher=Congressional Research Service |accessdate=29 August 2023}}</ref> canceled in the 2022 budget,<ref>{{cite news |url=https://www.military.com/daily-news/2021/06/04/it-may-be-end-of-line-navys-hypervelocity-projectile.html |title=It May Be the End of the Line for the Navy's Hypervelocity Projectile |last1=Seck |first1=Hope Hodge |date=4 June 2021 |accessdate=28 August 2023}}</ref> and tests continued in 2023.<ref>{{cite news |url=https://insidedefense.com/daily-news/army-executes-prototype-cannon-launched-hypervelocity-guided-projectile-sets-record |title=Army executes prototype cannon-launched, hypervelocity guided projectile, sets record |last1= Sherman |first1=Jason |date=29 March 2023 |accessdate=28 August 2023}}</ref>

=== Experimental vehicles ===
==== P-52 ====
The P-52 was a 52-caliber variant of M109A6 Paladin offered to South Korea by BMY Combat Systems in 1992. It was rejected by South Korea in favor of K9 Thunder. Proposal stage only.<ref name="K9 Developer Interview (2)">{{cite AV media |date=2015-10-15 |title=[첨단국가의 초석, 방위산업] 자주포의 새 차원을 열다 – K-9 천둥(2부) |language=ko |url=https://www.youtube.com/watch?v=Lh_CVAm3XNo  |archive-url=https://ghostarchive.org/varchive/youtube/20211222/Lh_CVAm3XNo |archive-date= 2021-12-22 |url-status=live|publisher=국방TV}}{{cbignore}}</ref><ref>{{Cite web  |title=[K9 14회] "우리 자주포 우리가 개발한다"며 미측 제안 거부 |url= https://kookbang.dema.mil.kr/newsWeb/20220418/2/BBSMSTR_000000100185/view.do |access-date=2022-06-05 |website=국방일보 |archive-date=4 April 2023 |archive-url= https://web.archive.org/web/20230404151106/https://kookbang.dema.mil.kr/newsWeb/20220418/2/BBSMSTR_000000100185/view.do |url-status=dead }}</ref>

==== M109L52 ====
Jointly developed by the Dutch firm RDM and the German firm [[Rheinmetall]], the M109L52 was first revealed in 2002. The main improvement was replacing the M126 series gun with the longer 52-caliber cannon from the [[PzH 2000]], thus the MTLS ammunition of the PzH 2000 can be used. Improvements to the loading system were also made, resulting in an increased rate of fire from 3 rds/min to 9–10 rds/min, able to be sustained for up to 2 minutes. A total of 35 rounds can be carried.

==== M109-52 ====
The M109-52 is a 52-caliber variant of M109 developed by BAE Systems by integrating Rheinmetall L52 cannon.<ref>{{Cite web |url=https://www.baesystems.com/en-us/product/m109-52-self-propelled-howitzer |title=M109-52 self-propelled howitzer |publisher=BAE Systems |access-date=2023-12-01}}</ref>

==== M1299 ====
{{Main|M1299 howitzer}}
The M1299 was a prototype [[self-propelled howitzer]] developed by BAE Systems in 2019 under the '''Extended Range Cannon Artillery''' (ERCA) program. It was based on the M109A7, and was primarily designed for the purpose of improving the M109A7's effective range.  One battalion of vehicles is planned to begin a year-long operational assessment in 2023. It was expected to be fitted with an [[autoloader]], which would have increased its rate of fire from 3 to 10 rounds per minute.<ref>{{cite web | url=https://breakingdefense.com/2020/03/new-army-cannon-doubles-range/ | title=New Army Cannon Doubles Range; Ramjet Ammo May be Next | date=6 March 2020 }}</ref><ref>[https://breakingdefense.com/2021/03/army-outlines-ambitious-schedule-for-robots-armor/ Army Outlines Ambitious Schedule For Robots, Armor]. ''Breaking Defense''. 19 March 2021.</ref> The M1299 was cancelled in March 2024 due, at least in part, to excessive barrel wear. Advanced ammunition developed for the M1299 will continue development, and the U.S. Army will look for existing alternatives to fulfil its re-evaluated long-range fire support needs.<ref>{{Cite web |last=Judson |first=Jen |date=2024-03-11 |title=US Army scraps Extended Range Cannon Artillery prototype effort |url=https://www.defensenews.com/land/2024/03/11/us-army-scraps-extended-range-cannon-artillery-prototype-effort/ |access-date=2024-03-22 |website=Defense News |language=en}}</ref>