The development of the 105 mm M101 towed howitzer can be traced back to 1919. It entered service with the US Army in 1940. Shortly afterwards the 105 mm Howitzer Carriage M2A1 was standardised.

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. The M101 105 mm howitzer was replaced in front-line US Army service by the M102 howitzer which in turn has now been replaced by the now BAE Systems Land Systems 105 mm Light Gun.

After the Second World War the complete weapon was redesignated the Howitzer, Light, Towed: 105 mm, M101 and M101A1. The M101 consists of 105 mm cannon M2A1 or M2A2, carriage M2A1 and recoil system (M2A1, M2A2, M2A3, M2A4 or M2A5). The M101A1 is identical apart from an M2A2 carriage. The difference between the 105 mm cannon M2A1 and the M2A2, is that the M2A1's muzzle end is straight and the M2A2's is bell-shaped. The M2A2 carriage is fitted with a main shield group composed of right and left upper and lower shields, right and left top flaps, a bottom flap, and left and right auxiliary shields; while the earlier M2A1 is equipped with left and right main shields and a top shield.

The barrel consists of the barrel assembly, breech ring and locking ring. The carriage is of the single axle split trail type with a drawbar for securing to the prime mover. The carriage consists of the equilibrator, shield, elevating mechanism, cradle gears, elevating arcs, traversing mechanisms, top carriage, wheels and trails. Fire-control equipment consists of a Telescope Elbow M16A1D with a magnification of ×3 and a 13° field of view, a Telescope Panoramic M12A7S with a magnification of ×4 and a 10° field of view and quadrant M4A1.

The M101 fires the following semi-fixed ammunition:

• APERS-T (M546) with the complete round weighing 17.35 kg, maximum muzzle velocity of 504 m/s and a maximum range (charge 7) of 11,600 m

• HE (M1) with the complete round weighing 21.06 kg, maximum muzzle velocity of 472.4 m/s and a maximum range (charge 7) of 11,270 m

• HE (M444) (carries 18 M39 grenades) with the complete round weighing 19.05 kg, maximum muzzle velocity of 472.4 m/s and a maximum range (charge 7) of 11,270 m

• HEP (M327) with the complete round weighing 15.17 kg, maximum muzzle velocity of 559 m/s and a maximum range of 8,685 m

• HERA (M548) (RAP) with the complete round weighing 17.46 kg, maximum muzzle velocity of 548 m/s and a maximum range of 14,600 m

• Illuminating (M314 series) with the complete round weighing 21.06 kg, maximum muzzle velocity of 472.4 m/s and a maximum range (charge 7) of 11,270 m

• Smoke (M60 series) with the complete round weighing 19.46 kg, maximum muzzle velocity of 472.4 m/s and a maximum range (charge 7) of 11,270 m

• Smoke (M84 series) with the projectile weighing 19.03 kg, maximum muzzle velocity of 472.4 m/s and a maximum range of 11,270 m

• APERS-T (M546) with a maximum range of 11,600 m

Details of the Nexter Systems (previously Giat Industries) upgraded M101 are given in a separate entry. The first customer for this was Thailand. In 1996 the Philippines became the second customer and ordered 12 upgrade packages from Giat Industries (now Nexter Systems). The total number of M101 systems upgraded by Thailand was 285. There is a separate entry under Thailand for the upgraded M101, which has the local designation of the M425.

Details of the M101 upgrade package from the Kia Machine Tool Company are provided in a separate entry. In addition to being in service with the South Korean Army it is believed that Chile (Marines) have taken delivery of 16 of these which have the designation of the K-178.

Details of the RDM Technology M101 are given in a separate entry. This is in service with Canada and Chile. There was also a self-propelled model called MOBAT but this did not enter production. RDM Technology closed down in 2004.

This is armed with an M2 or M2A1 howitzer with an elevation of +35°, a depression of -5°, and a traverse of 30° left and 15° right. It is believed that Pakistan may have 50 of these systems held in reserve.