Infantry Support and Anti-tank Weapons in  Latin America: 90mm and 105mm Recoilless Rifles

Infantry Support and Anti-tank Weapons in Latin America: 90mm and 105mm Recoilless Rifles

ABOVE: Salvadorian soldiers parade with M67 RCL. The U.S. supplied some 379 M67 RCLs to El Salvador between 1981 and 1992 to arm the soldiers, and became most important in the urban fighting for San Salvador and three other cities in November 1989. (J. Montes)

In October 2013, Salvadorian authorities discovered some 213 anti-tank projectiles hidden in an underground reservoir in the community of El Congo, in the department of Santa Ana, some 51 miles west of San Salvador. The arsenal was in good condition and it is believed it was destined to Mexican cartels. Los Zetas have been mentioned as the likely recipients. The grenades were M371A1 HEAT types, so the nature of the finding would suggest that a few M67 RCLs are also missing from a military warehouse. Indeed, in Central America, El Salvador is the only army that makes use of large numbers of M67 as the primary means of anti-tank and fire support for infantry platoons.

Israel supplied 8 RBY-Mk1 AT, and 8 RBY Recce variants to Honduras. In the AT variant, the turret can traverse 360 degrees, and up to 16 rounds of ammunition can be carried. The AAA variant carries a TCM-20 twin 20mm light anti-aircraft gun system and 360 rounds of 20mm ammunition. Mechanically, the Honduran RBYs have been updated to RAM standard. The V6 diesel engine is located in the rear. It has a semi-elliptical leaf spring-type suspension, with hydraulic shock absorbers. Power steering and power brakes have been added and the brakes are hydraulic.

This 90mm recoilless rifle weights 17 kg unloaded, and consists of a steel tube, open at both ends, much like the old Bazooka. The rear end of the cylinder is equipped with a lock and a Venturi nozzle. The gun is loaded by unlocking the bolt, and opening it to the right side. The M67 is a 90mm portable cannon working on the recoilless principle. It uses M371A1 HEAT ammunition, weighing 4.2 kg, and with a theoretical effective range against fortified targets of up to 2,000 meters, the M371 practice projectile, and the M590 TP APERS ammunition, which weighs 3.1 kg and it is loaded with about 2,400 steel darts, being able to reach a range of 200 meters. The weapon has a trigger grip. It comes with a basic M103 optical telescopic sight with 3x magnification, and with integrated range settings between 0 and 800m. The U.S. supplied some 379 M67 RCLs to El Salvador between 1981 and 1992 to arm the soldiers, and became most important in the urban fighting for San Salvador and three other cities in November 1989.

Honduran cavalrymen working on their M38C equipped with M40A1. These elements are members of the 1st Armored Regiment (RECABLIN). Today, a superiorly protected and mobile M1152P1 as base would be ideal. Infantry units could be equipped with M40A1 modified with a trailer similar to the Austrian 10.6 cm rückstoßfreie Pak, or similar. (DVIC)

Pounding Guerrillas with RCLs

That November 1989, FMLN guerrillas launched the “To The Top Offensive,” also known as “Out with the Fascists, Febe Elizabeth.” The attacks came on November 11, when some 2 to 3 thousand fighters descended from Ayutuxtepeque to San Salvador, and occupied the neighborhoods of Mejicanos, Ciudad Delgado, Soyapango, and San Jacinto, and later took positions at the high class neighborhoods of San Benito, Maquilishuat, Lomas Verdes and Escalon. They also attacked the oriental cities of Zacatecoluca, San Miguel and Usulután. The troops, fighting in the densely populated areas, brought their heavy and cumbersome M67 RCLs to open holes in the walls, to allow movement from house to house, backyard to backyard. They were also used to defeat heavy guerrilla positions.

Mexican Humvees equipped with M40A1. The High Mobility Multipurpose Wheeled Vehicle (HMMWV), commonly known as the Humvee, is a four-wheel drive military automobile produced by AM General. The up-armored M1152 with B2 armor kits would be a better option. (J. Montes)

The 90mm M67 was introduced in the early 1960s along with the heavier 106mm M40. It was a reliable and effective weapon, but somewhat large and heavy. It eventually was replaced with guided missile systems in U.S. service, but remained in service in areas of extreme temperatures. U.S. Rangers used M67 RCLs to destroy two BTR-60s approaching the tarmac at Point Salines Airport on the island of Grenada in 1983. Another two M67s were used by C Company, 5/87th Light Infantry, 193rd Infantry Brigade in Panama during Just Cause, just a month after it’s used in the streets of San Salvador by Salvadorian troops, in 1989. In Panama, U.S. troops used the M590 AP projectiles to soften up Panamanian positions. The M67 was resurrected in 2011, when units of the 4th Brigade Combat Team, 101st Airborne Division deployed to Afghanistan.

In Central America, the Guatemalan Army is said to have received some 64 examples. The weapon was more common in South America. However, most countries have exchanged the M67 for lighter Carl Gustav and/or RPG types. Argentinean units did carry it to combat around the Malvinas, and used it against the British during that confrontation.

Heavy Hauling Tools

The Argentineans also used a 105mm RCL of local design and construction to fight back the British in the South Atlantic. It is known that positions around Mount Longdon, in the Falkland Islands – defended by B Company, 7th Infantry Regiment, and two Marine Platoons – deployed the Model 1968 RCL during the war in 1982. Argentineans bombarded the approaching British’s 3 PARA with their 105 mm RCL during the engagement, managing to hit a Milan missile position with it. It is said that the weapon was widely used in the battles for the outer hills around Stanley as well. The Model 1968 entered service in 1968 with the Argentinean Army. The RCL is aimed through a stadia-metric rangefinder optical sight and it is equipped with a spotting FAL Automatic Rifle for aiming up to 1,200m range. The weapon can fire in the indirect mode to a range up to 9.2 km and in direct mode up to 1,800 meters. Its ammunition selection includes an 11 kg HE and a 15 kg HEAT projectile, with the last mentioned being able to penetrate up to 200mm of armor.

The Laser Homing Anti-Tank (LAHAT) missile seen in LAAD, Brazil. This semi-active laser homing guidance missile was developed by the Israeli industry with the idea to use the 105mm tube as a launching platform. Its hi-tech system is used to upgrade the M40A1. Israel has also developed the RAVEN- (RArefaction waVE guN), and improved friction- and spring-based recoil reduction/negation technologies, with the development of the High Impact Weapons System that can be used in the M40A2 when mounted on a turret. (J. Montes)

Rio Tercero Military Factory also developed and built the Model 1974 FMK-1, weighting 397 kg. Both types of RCLs rest on a two-wheeled undercarriage trailer for transport, which can be raised or lowered to fire in either a raised, medium, or low position. The weapon mount has an elevation between -7 to +40 degrees. Once deployed, the weapon uses a crew of 4. This weapon is also used by the Guatemalan Army, with 64 in inventory; along with 56 U.S. designed M40A1 RCL. It fires 105mm rounds, to include among others, a 16.6 kg HE round or a 14.7 kg HEAT, with a capacity to penetrate up to 400mm of armor. There are four types of ammunition developed specifically for the Model 1968 and Model 1974 FMK-1, and both are said to be able to fire U.S. M40 RCL ammunition as well. The weapons would also fire Chinese (HE & HEAT), German (HE-FRAG), Spanish (M-DN-11 FRAG) and Israeli (I-HEAT) ammunition. This is in addition to the standard M-581 APERS, M-344A1 HEAT, and M-346 HESH. Austria and Sweden developed the RAT-700 HEAT-T and the 3A HEAT-T, and both able to defeat 700mm armored plates at 2,000 meters, a cheap substitute to any AT missile.

U.S. Heavy Recoilless Type

Returning to those dark days of November 1989, in El Salvador, we found Ilopango Air Base in the outskirts of San Salvador under siege from all fronts. The Air Base was defended by the 2nd in the Southern part of the airfield, covering from Santiago Texacuangos, Changallo, and Santa Lucia neighborhoods; and 3rd Paratroop Squadrons defending the Northern, part from Cañas river, San Jose and Conacaste neighborhoods. An Air Base Security Unit had been established in January 1982, with two riflemen companies, and one AAA battery (6 M55A2 guns). A 3rd Riflemen Company was established in 1984, and a 4th was established in January 1986, and all forming the Air Base Security Battalion. In addition to securing the airport, these were assigned patrol duties along Chalatenango, in the region of San José Guayabal, and to provide convoy security to fuel convoys to San Miguel.

After heavy fighting from November 10 to the 13, the troops were exhausted. On the 13th, the Air Force used two C-123K and four C-47, to relieve and exchange the 2nd and 3rd PARA squadrons for the 1st and 4th from Comalapa, which allowed them to take the initiative on the 14th. The M40A1 RCLs, which were normally kept in fixed defensive positions around Ilopango, were hauled by the paratroopers’ Support Weapons Squadron, air base security battalion, and other troops advancing on Soyapango and Santa Lucia. These were used to bombard with direct fire fortified guerrilla positions in areas where air support could not be used. The RCLs had to be emplaced by hand, a tasks very difficult in normal circumstances, and almost impossible under combat conditions. The losses after three weeks of fighting were tagged on December 12 by the Planning Ministry disclosed that the fighting produced 64 civilians killed, 428 KIA from the Armed Forces, 17 paratroopers among them, and 1,526 KIA from the guerrillas.

U.S. troops firing tube-launched optically tracked wire-guided missiles to defeat the fortified position where Uday and Qusay Hussein were barricaded in Mosul. Perhaps a more economical option to the TOW would be a M40A2 gun upgraded with a comprehensive package to make it effective at maximum range, day and night, and all weather, along with reduced IR/blast signature. (U.S. DoD)

The M40 RCL followed the steps of the ill-fated M27 recoilless rifle. This weapon was a 105mm recoilless rifle developed in the 1950s, and rushed into service in time for the Korean War. An example was examined at the Colombian Army Museum, Candelaria, Bogota. It resembled the M40A1, but had trunnions that were mounted far to the rear, and are said to be part of the problem with the design. From the failed M27 design, the U.S. designed the M40 RCL, firing the same 105mm round as the M27, but categorized as 106mm to avoid confusion. In this manner, the M40 entered in service in 1955 as Battalion Anti-Tank (BAT) gun. It is a heavy weapon, and at 462 lbs. (209.5 kg) is usually mounted on a vehicle. This is convenient since the high signature of the back-blast gives the position of the gun away, and it would be useful to reposition before the enemy recovers and counterattacks. The M40A1 is one of the most important support weapons in Latin America, and one able to destroy almost any contemporary tank. Its effective range is 1,200 m, being able to perforate up to 450 mm of concrete with standard HEAT rounds. It continues to be used by relatively modern Latin American armies, such as Brazil, Chile, Colombia and Venezuela. The improved M40A1 is said to have a rate of fire of 5 rpm, and the standard round weights 17 lbs. (7.7 kg), having a maximum reach of 6,900 meters. Mounted on its standard M79 tripod, the gun has a traverse of 360 degrees, and an arc of elevation between -17 and +65 degrees. The M40A2 is a little heavier, at 485 lbs. (220 kg), and has a better range, being able to fire a HEAT round to a maximum range of 2,745 m, but a lower rate of fire of one round per minute.

In addition to the U.S. variants, the Santa Barbara 106mm RCL is common in Latin America. This is basically the U.S. A1 made under license in Spain, and it is similar in all respects to the U.S. counterpart. It can fire anti-personnel rounds to a maximum range of 7,600m. Israel has also supplied numbers of M40A1/A2 to Latin America.

M274 mechanical mule with M40A1. An alternative for use of light infantry and airborne units of small countries, such as those in Central America, would be to use trailers similar to the Austrian variant (10.6cm rückstoßfreie Pak), or the a Norwegian version (Kanon-Rekylfri 106mm) or even the Finnish type (95 Sinko 58-61), along with either the Israeli package, or the Bofors/Saab (Simrad LP101 laser sight and a KN250 light intensifier). (USMC Cpl. Jessica L. Martinez)

Mechanizing and Modernizing the M40A1

The weapon is too heavy for regular infantry to use, unless modified to facilitate is emplacement with a light towed two wheeled trailer. In fact, at least one of such devices it is known to have been developed in the U.S., but this was discarded in favor of the M274 mule. This 4×4 M274 tiny tractor became a weapon platform for airborne and light infantry battalions, and was more useful than the wheeled carriage. However, for small armies and where the M40A1/M40A2 is still used as weapon support for the infantry, and where mechanization is not the norm, the trailer can still be useful as already demonstrated by the Argentinean and Guatemala M1974 FMK-1 models.

The Austrian variant, the 10.6cm rückstoßfreie Pak (rPAK), and the Norwegian version, the Kanon-Rekylfri 106mm, were both mounted on a two-wheel undercarriage with adjustable height. In 1961 the Finnish mounted their own 95mm Sinko M1958 on a light two-wheel trailer that allowed it to be hauled by two men for positioning or repositioning. Modified as such, the weapon became the 95 S 58-61. In addition to the two-wheel trailer, some countries added a front protective shield, also a nice feature when being used by Infantry troops in a more exposed position – if much to WWII style. Off course, that kind of likely combat scenario should be considered. A light undercarriage on their M40A1 RCLs would have been a feature much appreciated by the Salvadorian troops since the M40A1 is not as easily deployed and redeployed by regular Infantry when mounted on its standard M79 mono-wheel tripod.

Salvadorian M240 with M40A1. The RCL can be reconfigured with a laser range finder compatible with Image Enhancing NVDs for evening and limited night time use; a Thermal Sight (TS) Command Launch Unit (CLU) could be useful, and an Israeli designed Spike Fire Control System (FCS), with a built-in Laser Range Finder/Laser Target Designator (LRF/LTD). (J. Montes)

Most common in Latin America has been the M40A1 mounted on light utility vehicles, such as M38C/CJ8 Jeeps. The M825 refers to the M151 MUTT variant with a M40 RCL in the rear. This vehicle was common in Mexico, Honduras, Guatemala, and almost universally in South America. The M38C and M825 were replaced in many Latin American countries with the Israeli version of the Jeep, the M240 Storm. Given that the M40A1/A2 when fired does shake and lift light platforms, other countries in Latin America, like Colombia, have switched to heavier vehicles such as the M642 Abir light truck. Mexico, and Honduras, and now likely to be implemented by Chile, the M40A1/A2 is being accommodated in the Humvee. This provides for a more stable platform on a highly mobile and maneuverable vehicle.

Another desirable modification would be to mount the M40A1 on an armored vehicle to provide protection to the crew and means to redeploy quickly. During the internal conflict, the Salvadorian Cavalry Regiment modified several CJ-8 jeeps with front plates and partial side plates to protect the crew, and the gun tripod rested on a raised pedestal to clear the windshield and allowing forward firing. The most simple modification today, in similar fashion to the Salvadorian CJ-8/M40A1, would be to place the M40A1/A2 on a raised platform to clear the cabin in the bed of a M1152 troop transport protected (TTP) variant or similar. In fact, Venezuela has developed the Tiuna 106mm weapons platform, a heavier variant of their Humvee look alike, reconditioned to fit the 106mm RCL. The Tiuna is a 4×4 vehicle equipped with a GM Vortec V8 5.3L made in Mexico, and matched to a 5-speed transmission. Although most M40A1 guns were obtained from Venezuela before Hugo Chavez time, the country is likely to receive replacements parts now from the Defense Industries Organization (DIO) from Iran, where the M40 is manufactured as the Anti-Tank Gun 106. The Venezuelan forces are also recovering and repowering their IAI/RAMTA RBY-Mk1 vehicles, at the Logistical Support 108 Battalion General de División José Escolástico Andrade from Ciudad Ojeda, Zulia. Although the RBY-Mk1 are being remodeled as AAA vehicles, with the TCM-20 Mk.5 (a match also realized with the Tiuna), the vehicle is also able to carry the M40 RCL.

Peruvian Army M1165 – an ideal platform to accommodate a modernized M40A1 RCL. As with the M1152, GM indicates that the M1165 provides superior protection for crew, weapons components, and ammunition. The armor is available in two kits: The “A” kit, which can be factory installed, and optional “B” kit, which when combined, provide gapless mine and ballistic protection. (J. Montes)

Effectively, Israel supplied 8 RBY-Mk1 AT to Honduras. The version applied all the above mentioned principles, encasing a 106mm recoilless gun on an open topped turret with a 360 degree traverse. The gunner and loader seat together, safely within the compact turret, and there are up to 16 rounds of ammunition ready for use in a compact, agile, highly maneuverable, and protected base. The platform was a mine resistant vehicle, with its wheels and axles placed as far forward and backward as possible, and the thickest, 10mm, steel armor was incorporated into the floor while 8mm steel armor protected the rest of the vehicle. The floor itself was V shaped. The vehicle weighted 3,600 kg, and remained open-topped, allowing for all sorts of weapons to be placed immediately behind the driver. These vehicles saw combat in early 1980s.

In February 1983, the Honduran Army had moved the 2nd Recce Squadron, 1st Cavalry Regiment, comprising two RBY ATs, three RBY scout vehicles, and three M-38C gunjeeps (eight vehicles), to San Lorenzo. On 29 April 1983, FMLN guerrillas wiped out defenses on the Salvadorian side of the Amatillo Bridge that separates Honduras and El Salvador. When the call for reinforcements came, the Honduran Army dispatched two platoons from A Company, 11th Infantry Battalion, along with the 2nd Recce Squadron to the bridge. These units occupied positions about 1 km away at Nancito Hill, with the 1st recce platoon taking the right (north) zone and the 2nd the left (south) zone. Once the counter-attack was ordered, they used their 106-mm rounds to destroy positions at 800 meters. The Hondurans also received a battery of three SOLTAM 160mm mortars, which continued to suppress the guerrillas. After the confrontation, an Armored Detachment (platoon)/Tank Squadron moved to Salamer valley near the 11th Infantry Battalion.

Original RBYs carried a Chrysler 225-2 V6 gas engine, but those in Honduran service have been upgraded to RAM V1 standards by repowering them with the Deutz BT6L 912S inline-V6 diesel engine, developing 132 hp, coupled to an Allison AT-540 automatic transmission, with 4 forward speeds and 1 reverse speed. The transfer case is a 2-speed Harwaythorn type, and the drivetrain has 4×4 capability. The fuel capacity is 150 liters to provide for an 800 km range. In El Salvador, several years ago, General Gustavo Perdomo came up with a similar idea and developed a gun truck using a Jupiter 7-ton truck equipped with a large open-topped turret encasing a M40A1. The turret had a 360 traverse but was too large, cumbersome, and provided little protection to be practical.

Guatemala M1974 FMK-1 105mm RCL. This weapon was developed and built by Rio Tercero Military Factory in Argentina. It weighs 397 kg, and rests on a two-wheeled undercarriage trailer for transport, which can be raised or lowered to fire in either a raised, medium, or low position. The weapon mount has an elevation between -7 to +40 degrees. Once deployed, the weapon uses a crew of 4. (José Turcios)

These examples proved that the idea to encase the M40A1 under protection persists. The Jordanian KADDB has probably produced the best solution, by accommodating the 106mm recoilless gun inside a compact turret mounted on top of an Al Jawad Vehicle. The RCL is aimed using a camera sight slaved to the gun and controlled from inside the protection of the armored turret; the image is displayed on an 10-inch screen to the gunner and a switch is used to fire the gun from inside. Presumably, the M1167 gunner protection kit (GPK) turret can be modified in similar manner. The ring mounted GPK provides a 360 degree arc of fire, and has been modified to dissipate the back-blast from a TOW missile. The GPK could function in the same manner of the KADDB-turret, or in a simplified manner with hi-tech sights.

In the 1980s, Bofors developed a modernization package that did away with the spotting rifle, and provided for first shot and first hit at maximum range (some 2,000 meters) capabilities. The package matched the Simrad LP101 laser sight and a KN250 light intensifier. The LP101 could be replaced for a modern Simrad LP10TL target locator, which according to the manufacturer is a fully integrated fire control solution. The lightweight KN250 is part of the Simrad KN200 intensifier series and night vision binoculars KDN250. These are; “clip-on units providing a night time capability to optical day sights. The night vision image is viewed through the eyepiece of the day sight. This allows the user to retain the same eye position, aiming reticule and magnification for both day and night use.”

The weapon is considered so viable that it remains in service even when a number of AT missiles are being incorporated. Chile uses an upgraded M40A1, and Venezuela uses the weapon in large quantities as well and has the means to upgrade it using Eastern European technology. Brazil, Colombia and Ecuador are three other countries that could end up upgrading their RCLs; while the Mexican and Central American armies could follow suit, along with Uruguay and Paraguay.

Two Salvadorian soldiers demonstrate how the M67 is loaded. This 90mm recoilless rifle weighs 17 kg unloaded, and consists of a steel tube, open at both ends, much like the old Bazooka. (FAES)

Cheap But Awesome Power

It fits that in environments where adobe and concrete structures are the norm, and where the enemy is unlikely to consist of massive armored formations with side troops hunting down anti-tank teams, the awesome firepower of high explosive ordnance is preferable and makes more sense than the more expensive high-tech missiles. The deadly beehive swarm of flechettes for close-in defense provides unique combat solutions as well.

The M40A1/A2 is still produced by several nations, including Pakistan. The Israeli variant is said to be fitted with a thermal sight and laser range finder/target designation system compatible with Image Enhancing NVDs. This is the result of combining the gun with gadgets of the Laser Homing Anti-Tank (LAHAT) missile. This semi-active laser homing guidance missile was developed by the Israeli industry with the idea to use the 105mm tube as a launching platform. The missile uses a tandem warhead with the capability to penetrate 800 mm up to 8 km away and can be used to engage extreme range targets, and where pinpoint accuracy is required. There is a LRF/laser designator module, and inclusion of LAHAT programming in the fire control computer. The LAHAT is stowed and handled much like any other 105mm round.

The Venezuelan Army perhaps could modify its M40A1 using technology developed for Russian AT missiles such as this Kornet-E from the Peruvian Army. This would be in a similar manner as done by the Israelis with their LAHAT missiles. However, this suggestion could apply only to the sights since the LAHAT has been designed specifically to be used in conjunction with the M40 as a launcher, while the Kornet-E has a 152mm diameter. (J. Montes)

Cost is a factor when engaging the enemy. On 23rd July 2003, U.S. troops hunted down Saddam Hussein’s sons in northeast Mosul. Army Lt. Gen. Ricardo Sanchez would later acknowledge that units of the 101st Airborne Division had fired ten tube-launched optically tracked wire-guided missiles to defeat the fortified position where Uday and Qusay where barricaded. The price of a TOW missile in 2000 was $180,000, so it had taken about $1,800,000, just for the cost of the missiles, to defeat the unworthy target. By comparison, in about the same time period, an 18.73 kg M-581 APERS (anti-personnel) round was said to have a cost of some $1,405; a 15.7 kg RAT-700 HEAT-T was some $530; and a 16.89 kg M344A1 HEAT was $380; and a 14.5 kg 3A-HEAT-T round was $450. Therefore, the fortified position would have been demolished for less than $10,000.

Definitely an argument to keep the M40A1/A2 around for some time.