Artillery: Extreme Mortar Precision

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April 30, 2021: The Israeli Army has ordered a new guided 120mm mortar shell, Iron Sting, that can use GPS or laser guidance to hit targets with greater precision than any existing guided shell. Iron Sting is also equipped to work with a new digital fire control system that is also entering wide use in the Israeli military. That means 120mm mortars, which are vehicle mounted, can receive target location data from any Israeli ground, air or naval source and quickly program and fire Iron Sting shell at anything within twelve kilometers. While GPS guidance is reliable enough to put the shell within a few meters (ten feet) of the target, laser guidance can reliably hit individual vehicles, bunkers or snipers in buildings. The laser guidance requires someone within a few thousand meters of the target to aim the laser at the target and keep it there for the laser guided shell to hit the reflected laser light. Another advantage of laser guidance is that is harder to jam than GPS. Some GPS jammers can disrupt GPS guidance within several thousand meters. Laser signal disrupters are more expensive and only provide protection for individual vehicles and similar size targets. Israel has been using GPS guided 120mm shells since 2015 and they cost about $33,000 each. Iron Sting is more expensive but considered more effective due to the laser guidance and integration with the new fire control system.

The Israeli guided mortar program became a competitor of the earlier American ATK guidance kit, which entered service with 155mm artillery shells in 2010 with American forces. A decade later a 120mm mortar version was introduced. ATK guidance systems were contained in a separate guidance system designed to replace the fuze that all artillery and mortar shells have, and is screwed into the front of the shell. The ATK devise is a larger fuze containing the precision guidance system (first GPS, then laser) and fins that move to put the artillery or 120mm mortar shell closer to the target. All you need to convert existing artillery or 120mm mortar shells to GPS guidance is the ATK or Israeli fuzes, which handles the usual fuze functions (setting off the explosives in the shell) as well as guidance.

To use the fuze type GPS systems, you place each fuze into a device that transfers the target GPS coordinates, then screw the fuze into the shell, and fire the shell. It would also be possible to program each fuze once it is screwed into the shell, via a metal probe that fits in a hole in the fuze, transfer the data, and signal that that the transfer was accurately made. The GPS guided fuze can put the shell within 6-10 meters (20-30 feet, and usually much less) of the coordinates entered. The new Israeli guidance system fuzes for mortars can be programmed more quickly.

Because of the GPS fuze, guided 120mm shells got a lot cheaper and easier to use. This is particularly crucial for 120mm mortars, which are used by units close to the front lines, where not a lot of ammo can be carried, and resupply is riskier since the enemy is so close. A guided 120mm shell means fewer shells getting fired to get the job done. Most vehicle mounted 120mm mortars carry about fifty 120mm shells and those vehicles can carry a dozen or more of the guidance fuzes to turn any of those fifty shells into a GPS or laser guided versions for use against targets that require only one or two shells rather than a barrage of a dozen or more shells landing over a wider area.

Unguided mortar shells cannot put the first round very close to the target, which means firing several rounds to adjust aim before one gets one on target. A guided mortar round is very useful in urban warfare, where a miss will often kill civilians. The 120mm mortar round has about 8 kg (17 pounds) of explosives, compared to 10 kg (22) pounds in a 155mm shell. The smaller explosive charges reduce collateral damage to civilians. Normally, an unguided 120mm shell will land anywhere within a 136-meter circle (on the first shot). All GPS guided rounds land within a ten-meter circle and laser guided shells land within a one-meter circle. The GPS guided mortar shells ares popular with the troops as are the earlier GPS guided 155mm artillery shells, 227mm rockets and JDAM bombs.

Excalibur, the first effective and widely used GPS guided shell did not enter service until 2007 with the guidance system built into a 155mm shell. In 2011 Excalibur 1A-2 became available as an extended range version. Excalibur 1A-2 could hit targets with precision up to 40 kilometers away with the M777 howitzer or 60 kilometers or more with guns using longer barrels or rocket boosted shells. Excalibur 1A-2 was particularly useful in Afghanistan, where the older (23 kilometer) shell was restricted by its short range. Guided rocket and shells have a longer effective range because unguided projectiles become less accurate the farther they go. With affordable and reliable projectiles, it was not possible increase the range these weapons could be used. This was particularly true of mortars, which never had much range to begin with.

In 2013 Excalibur got some cheaper competition from the ATK M1156 Precision Guidance kit that is screwed into the front of the shell like a fuze would be. The ATK fuze cost less than half as much as an Excalibur shell. Initially Excalibur shells cost $100,000 each. That has since been reduced to less than $70,000 a shell as has the cost of ATK fuzes. Excalibur is more accurate that the ATK approach, but not enough to prevent ATK fuzes from outselling Excalibur. Israel was slow to introduce guided shells for their 155mm artillery because Israel already had a growing number of small guided missile systems that seemed to take care of targets that had to be hit with the first attempt. For that reason, 120mm guided mortar shells entered Israeli service before guided 155mm artillery shells.

ATK first introduced its GPS guidance fuze for 120mm mortar shells in 2011 and this proved very popular (and successful) with the troops. This was because mortars are considered very effective infantry weapons, and most nations equip their troops with 120mm mortars as well as larger numbers of smaller caliber (50mm-82mm) mortars that are carried by infantry. While light enough to move with the troops, mortar ammunition has to be carried as well. A 120mm mortar shells weighs about 16 kg (35 pounds), which is why 120mm mortars are transported in and often fired from a vehicle. Only a few dozen shells are carried with each vehicle and ammo resupply is more difficult for the infantry than for the larger (105mm-155mm) artillery that is usually ten kilometers or more behind the infantry. The 120mm mortar guided shell is much more important because far fewer (one instead of six or more) shells are needed to deal with a target. When fewer shells are needed the limited supply of shells carried with a 120mm mortar can deal with more targets.

Oddly enough the modern mortar did not show up until Britain developed it in 1915, during World War I. This was in response to troops requiring some kind of artillery they could use from the trenches and carry with them when they advanced. At that time artillery was horse drawn and troops transmitted target information via telephone lines. Althugh these telephone wires were designed to lie on the ground and be deployed or repaired quickly, in combat the lines were frequently cut by enemy artillery fire. Thus, the need for portable artillery support, which the lightweight British mortar provided. These infantry mortars were widely adopted and improved after World War I. The first large American mortar was an 107mm model based on the British four-inch (102mm) mortar. The 120mm mortar was invented in France during the 1930s, and widely copied and used ever since.

The original 120mm mortar was too heavy, at 150-200kg (330-440 pounds) for the troops to carry long distances, but it was lighter than regular artillery and as effective as the 105mm howitzers which provided most of the firepower during World War II. Some 120mm mortars were mounted on wheels and could be pulled by horses or troops. In Western armies the 120mm and 107mm mortars were often carried in light trucks or jeeps and set up next to the vehicle for firing. Some of these heavy mortars were mounted and fired from armored personnel carriers, which were first used during World War II.

The US did not have a 120mm mortar during World War II and only had a 107mm (4.2 inch) model because that weapon was designed just for delivering chemical shells. Since chemical weapons were not used during World War II, with a few minor exceptions, the 107mm mortars didn't have much to do except deliver smoke shells, which some considered a "chemical" weapon, even though they provided concealment for friendly troops rather than casualties among the enemy. By the end of World War II, the 107mm mortar was firing high-explosive shells most of the time.

By 1944, it was recognized that the M2 4.2 inch (107mm mortars) were useful as artillery and they were used as such, even though they had a range of only 3-4 kilometers. Each "chemical" battalion contained 32 mortars and these were assigned to corps. This was quite different from the practice in other nations, where regiments were given 120mm mortars. One benefit of their past mission was that the battalions were equipped with white phosphorous (WP) shells. The WP shell created a lot of smoke, but the burning phosphorous caused nasty casualties. The Germans made noises about illegal use of "chemical weapons" when they realized what WP could do, but this did not result in the use of chemical weapons in retaliation. Nor were the Germans able to use many WP shells themselves because of raw material shortages.

As the war went on, it became the American practice to assign one mortar company (eight 4.2" mortars) to an infantry battalion. Not all infantry battalions got mortars, preference being given to units involved in attacks. An improved 107mm mortar, the M30, was developed after World War II and widely exported. Many nations still use it and the Americans did not adopt the 120mm mortar until 1991 when the Israeli Soltam was selected to replace the 107mm models. Israel, like most other nations, adopted 120mm mortars and Israel soon became a pioneer in developing new 120mm mortars, fire control systems and guided shells.

 


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