Artillery: Perfecting The 120mm Mortar

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September 4, 2012: The U.S. Marine Corps has ordered the first 42 PERM (Precision Extended Range Munition) 120mm mortar shells. These have a range of 17 kilometers and an internal guidance system that always has them land within 20 meters of where they were aimed. Several companies will be submitting their version of PERM and the most reliable one will be selected once the competition (which will take 24 months) is complete. This is all part of marine efforts to build a much better 120mm mortar.

Three years ago, after six years of development and paper shuffling, the U.S. Marine Corps finally ordered the first twenty production model EFSS ( Expeditionary Fire Support System). Earlier in 2009, six systems (each consisting of two vehicles, one 120mm mortar, an ammo trailer, and other gear) were issued to a marine artillery battalion for testing.

The goal with EFSS was to create a new lightweight, self-propelled artillery system. Initially, marine developers combined an existing commercial vehicle, the Supacat HMT (High Mobility Transport), with a 120 mm mortar system. The HMT is a seven ton, four wheel cross country vehicle with a capacity of 3.2 tons. It has a 180 horsepower engine and a 4x4 drive optimized for cross country work. The cab was modified to hold the five man gun crew.

There were considerable delays when it came time to figure out how to get the HMT into the MV-22 or CH-53E. The MV-22 was simply too narrow for the HMT or most other available vehicles. The marines had to get another vehicle, the ITV (Internally Transportable Jeep). This is a modified version of the Growler, a jeep like vehicle that usually sells for about $8,000. After all the needed mods were done with, the marines were paying about $100,000 for each ITV. The Growler is basically a modification of the old (replaced by the Hummer in the 1980s) M-151 Jeep.

The mortar weighs 818 kg and is mounted on a computer controlled turntable. The mortar can fire regular 120mm shells 8.2 kilometers, or rocket assisted ones 17 kilometers. This is not as far as a 155mm howitzer can reach but the marines feel that air power and rockets can handle longer range targets. The breech loading mortar system allows for rapid fire and the turntable system takes data directly from forward observers and quickly positions the 120mm tube to put the shells on the target. The EFSS can put shells on the target within minutes of a request. The system can fire 20 rounds in two minutes and uses a GPS assisted fire control system to provide accuracy comparable to any other artillery system.

The 120mm shells are also about half the weight of 155mm ones. This is to be overcome with a higher rate of fire and the use of several types of cluster bomb shells. One of these, for example, will destroy most armored vehicles and kill or wound most troops in a 100x100 meter area. Each of the 32 bomblets can penetrate four inches of armor but will be hitting the thinner top armor on armored vehicles.

The marines went after the 120mm mortar, instead of another 155mm howitzer, because the mortar is lighter, faster firing, more mobile, and, with the right ammunition, just as destructive as the larger howitzer.

 


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