The article below is a summary of an article written in French by Bernard Amrhein published in the armament engineers magazine n° 109 (http://www.caia.net/page/517/la-revue).
It was in 1915 on the front line and in the mud that Edgar William Brandt first sketched the plans for a lightweight and mobile howitzer to provide close combat support for frontline infantry. Since then, the army has always had a use for the mortar, a weapon that has been constantly modernised and has a promising future.
Invented in 1961 and developed by engineer Roger Crépin and his team, the Hotchkiss-Brand 120 mm Rifled/Towed mortar is still one of a kind. Considered by some as the best mortar in the world, it is in service in 25 countries, including five NATO members. Eminently fireable using diverse methods, it is particularly robust and fires a panel of five type of particularly efficient munitions. Equipped with a muzzle that is reputedly wear-free, the Mo 120 RT is also a perfect launcher, and timeless. It therefore seemed more sensible to work on the gunners’ real weapon: the ammunition. That is why TDA Armements, a Thales subsidiary, under the umbrella of the DGA French procurement agency, has undertaken to transform the existing 81mm and 120mm projectiles in order to render them insensitive to agressions and equip them with double security rockets. This project was also the occasion to refine the design of mortar ammunition in order to reduce the minimal range to 900m and increase the maximum range to 8,600m.
Launched in 1993, the embarked version of the Mo 120 RT essentially consists of an adaptation of the gun on a carriage that can absorb the recoil when it is fired, whilst maintaining the ability to use the whole range of pre-existing ammunition and by integrating this new weapon system on a given vehicle. As soon as the order to fire has been received, the vehicle opens its two roof traps whilst driving to its contingency firing position. Once it has stopped, the cannon automatically aligns the firing elements and the gunner places the first projectile on a crib that moves towards the front of the tube where a charging mechanism grips the projectile to introduce it into the ordnance. The gun can then fire up to 10 shots in a minute, then exits the battery whilst bringing the canon back into travelling position and shutting the traps. That means the gun has left its position before the first mortar has hit its target which makes any counter-battery fire technically impossible.
Today it is still necessary to fire in salvos or bursts to surround the target and ensure a military effect of destruction or neutralisation by recouping several bands of lethality of about 50m. As modern warfare is highly likely to take place in urban zones, it has become necessary to adopt a mortar guided munition (MGM) that will arrive on the target with a theoretical precision of less than one metre that has an optimised military charge which will only produce extremely limited collateral damages. Infantry units in Afghanistan were all deployed on the outskirts of hamlets or villages which interdicted the use of mortar projectiles or artillery with a ballistic trajectory that dispersed widely and whose effects are particularly lethal. With the MGM, it will be possible to destroy a high value target in a house. As a great range of targets will be able to be treated in the future with MGMs, it will become possible to drastically reduce the logistical weight of fire support units.