Development and designationEdit

After World War I, the U.S. Army Ordnance Department studied various captured German 105 mm-caliber howitzers and developed the 105 mm Howitzer M1920 on Carriage M1920. A box trail carriage design (the M1925E carriage) and two other split trail designs (the T1 and T2) were also developed, but the original split trail design was found superior after testing. After being selected, the piece was standardized in December 1927 as the 105 mm howitzer M1 on carriage M1. The Army had an intention to replace all 75 mm gun-howitzers in its divisional and non-divisional field artillery regiments with 105 mm pieces, but a lack of appropriations stalled the idea and eventually forced it to be completely abandoned by 1929; a limited plan developed in 1925 envisioned re-equipping three regiments, but by 1933, only 14 M1 howitzers had been manufactured,

A modified version of the M1 was trialed in 1932 which used semi-fixed ammunition instead of separate-loading ammunition. Since this development required a different breech block, the new piece was designated the 105 mm howitzer M2 on carriage M1. 48 pieces were manufactured in 1939. The original M1 carriage had been designed for towing using horses rather than trucks, and a new carriage, the T5 (M2), was developed in 1939 and standardized in February 1940. The breech ring of the howitzer M2 was modified in March 1940 before large-scale production began, creating the 105 mm howitzer M2A1 on carriage M2.^[1]

The weapon was heavy for its calibre but this was because the gun was designed to be durable. Thus the barrel and carriage could see great use and remain functional without wearing out.^[2]

The U.S. military artillery designation system was changed in 1962, redesignating the M2A1 howitzer the M101A1. The gun continued to see service in the Korean and Vietnam Wars. Though a similar model, the M102 howitzer, shared the same roles in battle, it never fully replaced the M101A1. Today, the M101A1 has been retired by the U.S. military, though it continues to see service with many other countries. By the end of the Second World War, 8,536 105 mm towed howitzers had been built and post-war production continued at Rock Island Arsenal until 1953, by which time 10,202 had been built.

AustraliaEdit

M2 Howitzers are still in limited service in the Australian Army Reserve, but are being replaced with 81-millimetre (3.2 in) mortars with an emphasis on the retention of indirect fire support skills.^[3] In regular service they were replaced by the 105 mm L119 Hamel gun and the 155-millimetre (6.1 in) M198 howitzers.

CanadaEdit

The Canadian Forces used the M2A1 as the C2 howitzer until 1997, when a modification was made to extend its service life; it is now designated the C3. The changes include a longer barrel, a muzzle brake, reinforced trails and the removal of shield flaps. It remains the standard light howitzer of Canadian Forces Reserve units. The C3 is used by Reserve units in Glacier National Park in British Columbia as a means of avalanche control.

CroatiaEdit

A number of M2/M101 howitzers were used by the Socialist Federal Republic of Yugoslavia and approximately 50 were inherited by Croatia, of which four are still in use for training with the Croatian Army.^{[citation needed]}

FranceEdit

The French Army used the M2 howitzer, designated HM2, in the Algerian War^[4] and during the Opération Tacaud in Chad.^[5] France later supplied a battery of HM2 to the Rwandan Armed Forces during the Rwandan Civil War that led into the Rwandan genocide.^[6]

PhilippinesEdit

Several M101 howitzers are still in use with the Armed Forces of the Philippines and is normally used to battle rebels in Luzon, Visayas, and Mindanao. It was also used in direct fire against Islamic militants during the Battle of Marawi.

South KoreaEdit

In 1950, South Korea received 13 M2s to supplement and replace the M3 howitzer. By the end of the Korean War, 1,127 howitzers were transferred from the United States; three artillery battalions equipped with the M2A1 were assigned to every infantry division.^[7]

In early 1970s the Republic of Korea Armed Forces needed to replace these old howitzers due to the maintenance burden. To balance North Korea build up of artillery, South Korea decided to invest in its own arms industry to equip its large military cost efficiently. Following the success of Project Thunder I for smaller caliber weapons supported by United States Department of Defense assistance, in April 1972 the South Korean president Park Chung-hee ordered Project Thunder II for larger caliber weapons including a 105 mm howitzer. The United States refused to cooperate due to the then diplomatic overtures to the People's Republic of China. The United States Embassy in South Korea ordered its technical team to end assistance. The US believed South Korea lacked the tooling and knowledge to develop the weapons on its own. The Agency for Defense Development however reverse engineered the M2A1 (M101A1) howitzer and production of prototypes began in March 1973.^[8][9]

On 25 June 1973, three prototypes were demonstrated publicly. After the test, the United States ambassador Philip Habib arranged the meeting of South Korean chief secretary O Won-cheol and colonel Montgomery from the Joint U.S. Military Affairs Group-Korea. The colonel provided technical review of the howitzer, which was collected by the US intelligence, and concluded the howitzer is not compatible to the US standard—recommending the purchase of US equipment for logistics support in joint operation. South Korea refused and pursued for domestic design; however in September 1973, the two nations signed an agreement for technology transfer. It was the first weapons research cooperation between the two nations, and the South Korean defense industry began to form with guidance from the United States.^[8][9]

In February 1974, hostilities grew after North Korea sunk a South Korean fishing boat and kidnapped fishermen near Baengnyeong Island. As a response, 10 howitzers crafted prior to the US support were sent to the island, but pulled out after severe malfunctions during operations. On November 1975, the reinforced variant experienced barrel breakdown; the failure led to the invitation of American engineers in January 1976 for overview on South Korean facilities. After 1.5 months of inspection, the engineers suggested the Eighth United States Army to replace the Korean copy by producing original M101A1 in South Korea. The United States then provided its sophisticated technical data package to South Korea, which quickly readied mass production of the howitzer before the year ends. The production began in 1977 as designation KM101A1 by Kia Machine Tool (now Hyundai Wia) in Changwon.^[10][11]

In 1978, South Korea restarted domestic howitzer program based on M101. The howitzer applied 38 calibers barrel for extending the maximum range to 18 km using RAP ammunition. Only 18 howitzers saw service with South Korean military in favor of mass producing KH179 155 mm Towed Howitzer.^[11]

As of 2021, South Korea is the largest operator of the M101 howitzer with about 2,000 pieces in active service. It is planned to convert 1/3 of its inventory to K105A1 self-propelled howitzer.^[12]

VietnamEdit

France and the State of Vietnam used M2A1 howitzers during the First Indochina War, as did the Viet Minh guerilla forces they fought against, who were supplied with at least 24 by the People's Republic of China, along with other captured American artillery pieces and mortars formerly operated by both Nationalist Chinese forces (the Kuomintang military) and US troops fighting in Korea.^{[citation needed]} Today upgraded M2A1 howitzers (some of which have been mounted on trucks and employed as self-propelled artillery) are still being used by the People's Army of Vietnam (the PAVN).^[13]

Other usesEdit

In addition, the M101 has found a second use in the U.S. as an avalanche control gun, supervised by the US Forest Service and the US Army TACOM's cooperative effort in the Avalanche Artillery Users of North America Committee (AAUNAC). The M101 is used by a number of ski areas and state departments of transportation for long-range control work. Under the designation of M2A2, the 2nd Battalion, 2nd Field Artillery Regiment, 428th Field Artillery Brigade performs salutes with 7 guns with World War Two Medal of Honor recipient names on their barrels.^[14]

Two M2 howitzers (1942) are still employed in providing the gun salute at Kristiansten Fortress, in Trondheim, Norway. M101/M2 is one of three approved salute guns in the Norwegian armed forces, and have been reduced to a caliber of 75 millimetres (3.0 in) for this purpose. They are used for gun salute also at Rena and Setermoen.^{[citation needed]}

Five M101A1 howitzers are owned by the Virginia Military Institute and are used for parades, evening retreat and other ceremonies.^{[citation needed]}

Two M101A1 howitzers are utilized by Palmetto Battery of the South Carolina Corps of Cadets at The Citadel for firing during parades. Officially, these guns are still property of the U.S. Army.^{[citation needed]}

Gun variants:

• M1920 – prototype.^[15]
• M1925E – prototype.^[15]
• T2 prototype, standardized as M1.^[15]
• M2 (1934) – minor changes to the chamber to allow the use of fixed ammunition.^[15]
• M2A1 (1940) – modified breech ring.^[16]
• M3 – lightweight howitzer, with barrel shortened by 27 inches (69 cm).
• T8 prototype (standardized as 105 mm M4 Howitzer in September, 1943) – vehicle-mounted variant with modified breech and with cylindrical recoil surface.^[17]
• M101 – post-war designation of M2A1 on carriage M2A1
• M101A1 – post-war designation of M2A1 on carriage M2A2
• M2A1 modernized variant by Yugoimport SDPR with max range of 18.1 km and 8 rds per minute^[18]
• C3 – Canadian C1 (M2A1) with lengthened, 33-caliber barrel
• KM101A1 - South Korean license of M101A1, 1977
• KH178 105 mm Towed Howitzer - South Korean 38 calibers variant, 1983

Carriage variants:

• M1920E – prototype, split trail.^[15]
• M1921E – prototype, box trail.^[15]
• M1925E – prototype, box trail.^[15]
• T2, standardized as M1 – split trail, wooden wheels.^[15]
• M1A1 – M1 carriages rebuilt with new wheels, brakes and other parts.^[16]
• T3 – prototype.^[15]
• T4 – prototype.^[15]
• T5, standardized as M2 (1940) – split trail, steel wheels with pneumatic tires.^[15]
• M2A1 – electric brakes removed.^[19]
• M2A2 – modified shield.^[19]
• XM124 & XM124E1 Light Auxiliary Propelled Howitzer – prototype (1962–1965) – produced by Sundstrand Aviation Corporation, who added an auxiliary drive system for local maneuverability (See also similar XM123 Medium Auxiliary Propelled 155 mm Howitzer with similar configuration). The base XM124 provided two 20 horsepower (15 kW), air-cooled engines, while the XM124E1 provided a single 20 horsepower (15 kW) engine and electric steering.
• M2A2 Terra Star Auxiliary Propelled Howitzer – prototype (1969–1977) – Lockheed Aircraft Service Company added an auxiliary drive system and a tri-star wheel system to the carriage of an M2A2 105 mm Light Howitzer to provide local maneuverability. The last surviving example is at the Rock Island Arsenal Museum.

•  

  Canadian soldiers fire a high explosive round with a C3 howitzer in 2009.

•  

  Royal Thai army M101 with new barrel.

•  

  XM124E2 Light Auxiliary-Propelled 105 mm Howitzer at the Rock Island Arsenal museum

•  

  The only surviving prototype M2A2 Terra Star Auxiliary Propelled Howitzer at the Rock Island Arsenal Museum. Note the tri-star wheel system and auxiliary drive system on the right trail leg.

•  

  Greenup, Kentucky, US

•  

  M101 A1 on display at Patriots Point Naval and Maritime Museum

• Medium Tank M4A4E1 – M2A1 in mount T70.^[20]
• Medium Tank M4(105), M4A3(105) – M4 in mount M52.^[20]
• Medium/Heavy Tank M45 – M4 in mount M71.^[21]
• Experimental mount on Holt tractor – ^[22]
• Experimental chassis designed by J Walter Christie – M1920.^[22]
• 105 mm Howitzer Motor Carriage T9 (based on Cletrac MG-2 tractor).^[23]
• 105 mm Howitzer Motor Carriage T19 (based on M3 halftrack) – M2A1.^[24]
• 105 mm Howitzer Motor Carriage T32 / M7 – M2A1.^[20]
• 105 mm Howitzer Motor Carriage T76 / M37 (Light Tank M24 chassis) – M4 in mount M5.^[23]
• 105 mm Howitzer Motor Carriage T88 (76 mm GMC M18 chassis) – M4 in mount M20.^[25]
• K105HT 105 mm howitzer mounted on an armored 5-ton truck system built by Samsung Techwin for the Republic of Korea Army (initially called EVO-105)
• Vietnamese M101 howitzer mounted on an Ural-375D 6×6 truck.^[26]

The gun fired semi-fixed ammunition, with 105 mm Cartridge Case M14. The propelling charge consisted of a base charge and six increments, forming seven charges from 1 (the smallest) to 7 (the largest). Use of M1 HE rounds prepared for the 105 mm howitzer M3 (same projectile and cartridge, but different propelling charge) was authorized.^[27]

HEAT M67 Shell was originally designed as fixed round, with Cartridge Case M14 type II. It was later changed to semi-fixed type with the standard cartridge, but with non-adjustable propelling charge. For blank ammunition, a shorter Cartridge Case M15 with black powder charge was used.^[27]

•   South Vietnam

• List of U.S. Army weapons by supply catalog designation (SNL C-21)
• M3 howitzer – Shortened barrel variant of M2 howitzer.
• M102 howitzer – The US partial replacement for M101 howitzer.
• KH178 105 mm Towed Howitzer – South Korean 38 calibers variant of M101A1.
• L118 light gun – British 105 mm howitzer.
• M119 howitzer – The US license of L118, replacement for M101 and M102 howitzer.

• Hogg, Ian V. (1998). Allied Artillery of World War Two. Crowood Press, Ramsbury. ISBN 1-86126-165-9.
• Hunnicutt, R. P. (1971). Pershing: A History of the Medium Tank T20 Series. Feist Publications.
• Hunnicutt, R. P. (1992). Stuart: A History of the American Light Tank. Presidio Press. ISBN 0-89141-462-2.
• Hunnicutt, R. P. (1994). Sherman: A History of the American Medium Tank. Presidio Press. ISBN 0-89141-080-5.
• Hunnicutt, R. P. (2001). Half-Track: A History of American Semi-Tracked Vehicles. Presidio Press. ISBN 0-89141-742-7.
• Technical Manual TM 9-1325, 105 mm Howitzers M2 and M2A1; Carriages M2A1 and M2A2; and Combat Vehicle Mounts M3 and M4. War Department, 1944.
• Technical Manual TM 9-1901, Artillery Ammunition. War Department, 1944.
• Technical Manual TM 9-1904, Ammunition Inspection Guide. War Department, 1944.
• Technical Manual TM 9-2005 volume 3, Infantry and Cavalry Accompanying Weapons. War Department, 1942.
• International Institute for Strategic Studies (February 2016). The Military Balance 2016. Vol. 116. Routlegde. ISBN 978-1-85743-835-2.

• Two Guns For One, November 1942, Popular Science one of the earliest detailed public article published on the M101 Howitzer
• FAS Military Analysis Network