During WWII, M1 and M9 "Bazooka" rocket launchers were considered good weapons, although their penetration was inadequate to reliably penetrate medium tanks, and nearly useless against their front armour. American engineers decided to solve this problem by increasing the caliber of the weapon. Work began in 1943, but mass production of the new RPG only got off the ground after the start of the war in Korea, where old bazookas proved ineffective against the T-34-85.
The experimental 3.25" (82.6 mm) T16 anti-tank grenade launcher was undergoing trials in the US in 1943. Modern American researchers note that no descriptions of photographs of the T16 survive to this day, and theorize that the experimental launcher could have looked like an enlarged M1 with a one piece barrel. The creation of a two piece M9 launcher prompted the designers to improve the enlarged version in a similar way. When the Americans captured 88 mm German Panzerschrecks in Italy in 1944, they decided to increase the caliber of their own weapon.
Work on the T74 3.5" (88.9 mm) RPG began in October of 1944. Its barrel was made from an aluminium alloy, just like the barrel of the M18 launcher, which made the new weapon lighter than the 60 mm M9 RPG. This work resulted in the adoption of the M20 rocket launcher (unofficially called "Super Bazooka". However, the US Army did not feel a pressing need to improve their anti-tank weapons after the conclusion of WWII. Small scale production of the Super Bazooka began in 1948, and full mass production began only in August of 1950.
The M20 rocket launcher was based on the M9A1. Like its predecessor, it had a tube barrel that was separated into two parts. The front half contained the flash suppressor, two clips for connecting the halves of the barrel during travel, and a shroud with a protrusion for connecting the halves in combat. The rear half had a bracket and a clip for connecting the pieces during travel, a shroud with a clip for connecting the pieces in combat, the trigger, the sights, the shoulder stock, the rocket fixation clip, and the spring contacts. To prepare the weapon for battle, the operator had to insert the shroud of the front half into the shroud of the back half and rotate until a click (1/3rd of a revolution).
The old and the new: M20 with the M28 rocket (left) and M9A1 with an M6A3 rocket (right).
Early Super Bazookas used a magneto trigger mechanism identical to the one on the M9A1. Later, it was replaced with a dual action mechanism (the generator worked when the trigger was pressed and when it travelled back to its initial position after being released), which tripled the amount of current that was generated. The safety button was moved from the rear of the pistol grip to the left side. The previous model only opened the electric circuit, but this one also blocked the trigger. The wire from the trigger mechanism ran towards a metallic shroud with two contact springs, located on an insulated pad near the rear opening.
The M20 was equipped with two sights: a collimator sight on a movable mount and a fixed iron sight. Initially, the collimator had a grid with concentric circles and ellipses. The matching iron sights had markings from 0 to 900 yards (823 m). Later, a sight with a vertical dashed line crossed with five horizontal lines of six segments each was used. The horizontal lines matched ranges from 0 to 400 yards (366 m), and their segments allowed for correction for the target's speed of up to 30 mph (48.3 kph). The new iron sights had one marking for 450 yards, and then markings for 500 to 900 yards. As old launchers were sent in for repairs, they received new sights.
The shoulder stock, as on the M9A1, was built from a curved metal strip. The front part had a collapsible screw, which, combined with a bipod, allowed the launcher to be firmly mounted at a fixed position. In practice, these attachments saw little use, and the screw and bipod were later removed.
The M20B1 modification was released alongside the M20. In American nomenclature, the letter B indicates a weapon with equivalent characteristics, but with a different manufacturing process. The M20B1 had its flash suppressor, rear opening guard, and connector shrouds built as one with their respective barrel halves. On the M20, they were attached with screws. The shoulder stock was screwed into the barrel. The new launcher was about half a kilogram lighter than the old one.
M20A1B1 RPG. 1 - front barrel half, 2 - collimator sight, 3 - rear barrel half, 4 - ignition mechanism wire, 5 - contact box, 6 - strap, 7 - shoulder stock, 8 - magneto, 9 - trigger mechanism, 10 - trigger guard, 11 - trigger, 12 - flash suppressor, 13 - universal wrench.
M20A1 and M20B1A1 modifications appeared in the last few months of the Korean War. They had a new, more reliable contact device, an improved rocket retention clip, a more comfortable shoulder stock, and other improvements. The barrel halves were interchangeable among all Super Bazookas.
The main round for the Super Bazooka was the M28 rocket, which was composed of a HEAT warhead, an M404 fuse, a rocket engine, and a stabilizer. The warhead with a conical copper insert was filled with a mix of cyclonite and TNT known as "Composition B". The fuse was inserted into the rear of the rocket, forming the middle of the projectile, and the rocket engine was screwed into the rear. The engine consisted of 12 tubes, grouped into 4 groups of 3. The tubes were ignited by the M20 electric igniter, which consisted of a plastic box with a detonator and a load of black powder. The fuse had a safety feature: a pin, which was held in place during transport by a retaining clip. The clip was removed during loading, and the pin was held in place by the wall of the barrel. After the rocket left the barrel, the pin fell off. The M28A1 rocket was also produced, which had a different stabilizer fin shape.
M29 and M29A1 rockets were used for training. They had inert warheads and a dummy detonator, equipped with a safety pin, to be as close as possible to reality. There was also a 27 mm T265 training rocket, which was not widely used, as it did not offer a realistic loading and firing procedure.
The change in the contact device of the M20A1 and M20B1A1 launchers resulted in the need for a new rocket: the combat M28A2 and training M29A2. They could be fired from old Super Bazookas, but the new launchers could not use old rockets.
M28A2 rocket. 1 - warhead, 2 - HEAT insert, 3 - explosive filler, 4 - safety, 5 - fuse, 6 - rocket, 7 - stabilizer fin, 8 - contact ring, 9 - rim.
T127E2 and T127E3 (later standardized as M30) smoke rounds were built based on the M28A2 fin section. The warhead design was altered. The thinly walled warhead was filled with white phosophorous, and the tip was empty to maintain balance.
The most effective round was the M35 HEAT rocket, introduced in the mid-1950s. While the previous rockets were based on WWII designs, the new weapon was closed to modern RPGs. The grenade received a new smaller ballistic cap, as well as a piezoelectric M408 fuse. Its front part contained a piezoelectric element, which was connected to the bottom of the rocket with wires, where the electric detonator and a range adjustment mechanism (the fuse could be armed at a range of 7-12 meters) were housed. A pin protected the fuse mechanism during transport. The rocket engine contained 19 tubes with a higher rate of burning. Because of this, the powder burned up in the barrel even at low air temperatures. The range of the M35 rocket was 30% higher, and the penetration was higher as well. It could not be used in old M20 and M20B1 launchers, only in the new M20A1 and M20B1A1.
Super Bazooka in combat
Even though M20 and M20B1 launchers were accepted into service in 1948, only a handful of units in the US and West Germany had them a few years later. Only the TO&E for infantry companies had the new launchers, all other units were still equipped with the old M9A1. The Super Bazooka crew consisted of four men (operator, assistant, and two ammunition carriers) and was included in the infantry heavy weapons section, which also included the M1919A6 heavy machinegun.
Super Bazooka operator, ready for firing.
The first three US Army divisions that were sent to Korea after the start of the war (1st Cavalry, 24th and 25th Infantry) were completely equipped with old RPGs. When it turned out that Bazookas were helpless against the T-34-85's front armour, a batch of M20 launchers was sent to Korea. They were first used on July 18th, 1950, at Daejeon. In this battle, the 24th Infantry Division claimed 8 knocked out T-34s. Starting with August of 1950, all US Army and Marine units arriving in Korea were fully equipped with M20 or M20B1 launchers. Units that were already in Korea were quickly reequipped. Thousands of M9A1 launchers were sent to warehouses, where some of them later became trophies for the North Koreans, and were used in combat. It turned out that they could not penetrate the front armour of the M26 Pershing, but were sufficiently effective against the M4A3 Sherman.
The North Korean army lost 239 T-34-85 tanks and 74 SU-76M SPGs during the Korean War. The vast majority of them fell victim to American aircraft. The infantry used their RPGs against tanks in very rare cases. More often, the rockets were fired at fortifications. In this role, they were more effective than 105 mm recoilless guns.
A US Army Sergeant demonstrates the M20 RPG to his Australian colleague.
The organization of the American infantry platoon was changed in May of 1952. A second heavy machinegun crew replaced the RPG team. Now, the RPG was subordinate directly to the platoon commander. However, as the Korean War transitioned into the positional phase, the number of Super Bazookas began to decrease. Towards the end of the war, only a quarter of American units had the authorized amount of RPGs. The main fire support weapon was the M18 57 mm recoilless rifle, which had a greater range and superior precision when compared to the M20. The heavy mass of the rifle was irrelevant in the static combat, and a lower weight of the shells was made up by their volume, especially since the unchanging front line allowed for steady supplies of ammunition.
The Texan National Guard on exercises. The RPG operator is carrying an M20B1A1 launcher collapsed for travel.
In 1958, the Super Bazooka team returned to the infantry platoon heavy weapons section. Its number was reduced to three men (there was now only one carrier). Two RPGs were included in the company HQ, and two in the heavy weapons platoon HQ. Another reorganization happened in the early 1960s. Now there were two RPG teams of two per section, with one carrier between them. The Super Bazookas were phased out for new 90 mm M67 RPGs. Old launchers remained in the company HQ (one) and in the platoon HQ (two), but they were replaced with disposable M72 launchers in the mid 1960s.
US Marines RPG team with an M20B1A1 launcher.
Super Bazookas were company level weapons in the Marines. The assault section of the weapons platoon of an infantry company had six M20 RPGs with a team of two servicing each.
By the start of the Vietnam War, the US Marines still used M20A1 (M20B1A1) RPGs, and they were also lingering in some Army units. Most RPGs were sent to warehouses upon arrival, as they were not needed. Later, they were issued as required, such as when bunkers had to be destroyed.
British Marines with an M20 Mk1 RPG in Kuwait, 1961.
Aside from the USA, Super Bazookas were supplied to their allies. British Commonwealth nations used this weapon from the Korean War to the mid-1960s, when they were replaced by Swedish Karl Gustav RPGs. In British nomenclature, the M20 was indexed M20 Mk1, and the M20A1 was the M20 Mk2. In France, the Super Bazooka remained the infantry platoon's standard anti-tank weapon until the early 1970s. The French Army used its Super Bazookas during the colonial wars in Indochina and Algiers. The M20 and its variants were used by West Germany, Sweden, Turkey, Portugal, Austria, India, Pakistan, South Korea, Taiwan, Philippines, Burma, and a number of other nations, including nearly every state in Latin America. In his book Guerrilla, Che Guevara honours the bazooka with a separate paragraph.
"The bazooka is a powerful weapon, which can be used by guerrilla fighters due to is simplicity. Of course, it must first be captured from the enemy. The bazooka is ideal against armoured targets and unarmoured troop transports, as well as capture of large military bases by small teams in a short period of time. The mass of the ammunition is a significant drawback. One man can only carry three rounds."
The M20 was a source of inspiration of many foreign designers. In 1951, the Super Bazooka was copied in China and produced as the 87 mm Type 51 RPG. From 1952, it was used in Korea, and a small number ended up in Vietnam. In Brazil, the Hydroar company produced a copy of the M20A1B1 with a battery instead of a magneto (like on the first bazookas). The Spanish M65, French F1 LRAC, and Belgian RL-83 Blindicide were inspired by the M20.