The M101A1 is a light, towed cannon that fires a 105mm (4.2-inch diameter) projectile. It is deployed in the field when the use of the 155mm howitzer is not practical.

The M101A1 105mm Light Howitzer can be used for direct (line of sight) or indirect fire. The cannon consists of a tube assembly, breech ring and locking ring, and is mounted on the recoil sleigh assembly. The firing mechanism is activated by pulling a lanyard.

The cannon is single-loaded and air-cooled, and it uses semi-fixed ammunition, which can be adjusted for distance and target. The carriage has a single axle and split trail. The trails are divided when the weapon is positioned and set up, drawn together and locked during travel. The recoil mechanism is a constant hydro-pneumatic type shock absorber, installed in the cradle of the carriage.

A maximum rate of fire of 10 rounds per minute can be reached. A sustained rate of 3 rounds per minute is possible with a capable crew.

Nexter Systems has developed, as a private venture, a modernisation package for the US 105 mm M101A1 towed howitzer, which is used by many countries. The kit has been developed by Nexter Systems (formerly Giat Industries) at facilities in Bourges where all production of artillery and tank barrels in France is undertaken.

The modifications can be carried out by Nexter Systems or the company can supply kits to enable the user to upgrade in his own facilities using his own personnel.

The modernisation includes replacing the original US-made 105 mm barrel with the more recent Nexter Systems LG1 Mk I/II Light Gun already in service with Belgium, Canada, Indonesia, Singapore and Thailand. The Nexter Systems M101A1 upgrade package involves:

• Replacing the existing 105 mm/23 calibre barrel with a new 105 mm/30 calibre barrel whose ballistics are identical to those of the latest 105 mm LG1 Mk II weapon

• Fitting this barrel with a double-baffle muzzle brake so as not to increase the forces on the recoil mechanism, which is retained in this upgrade

• Replacing the existing equilibrator

• Adding two ballasts on the trails

• Installing a breech that is identical to the original but made from a new steel that has been designed to withstand the pressures of longer range 105 mm projectiles

Nexter Systems have stressed that there is no modification of the gun structure, or of the recoil mechanism in their upgrade package.

The upgraded M101A1 is 233 kg heavier than the standard weapon but can fire all standard NATO ammunition including the old US M1 projectile to a maximum range of 11,400 m. It can also fire the more recent Nexter Munitions 105 BB base bleed projectile to a range of 18,500 m or a Nexter Munitions HB HE projectile to a maximum range of 15,000 m. It can also fire the new Nexter HE ER G2 round to a maximum range of 19,200 m after changing the breech ring.

In mid-1996, Nexter Systems announced that it had been awarded a contract from the Philippines to upgrade a first batch of 12 old US-supplied 105 mm M101 towed artillery systems.

These were upgraded in a number of key areas including the replacement of the current barrel with the new barrel, similar to that fitted to the Nexter Systems 105 mm LG1 Mk II light gun used by Belgium, Canada, Indonesia, Singapore and Thailand.

The Philippines is the second customer for the upgraded M101, the first being Thailand who ordered a total of 285 kits, all of which were delivered to Thailand by early 1997. Thailand has also taken delivery of significant quantities of 105 mm HE-BB (High-Explosive Base-Bleed) rounds from Nexter for use with these upgraded M101 weapons and the more recently acquired LG1 Mk II Light Guns covered in detail in a separate entry.