55 S 55 (from Finnish55 millimetrin sinko vuodelta 1955, '55 millimetre recoilless anti-tank weapon model 1955'),[2] colloquially kevyt sinko and nicknamed Nyrkki,[3] was a Finnish recoilless anti-tank weapon from the mid-1950s. The 55 S 55 was designed by a Finnish Defence Forces team led by MSc, Capt Esko Puronto, and it was manufactured by FDF's Vammaskoski factory (now part of Finnish state military industrial enterprise Patria).[3]
During the later stages of World War II, Finland received large shipments of German Panzerfaust (F1 and F2) and Panzerschreck. These weapons were used after the war, but soon the need for modern replacement arose.[3]
After the World War II, short-range anti-tank weaponry was seen as the most important anti-tank weaponry by the Finnish Defence Forces, and it was seen that the further the short-range weaponry could be developed, the less there would be need for the more expensive long-range weaponry. Finland's forested areas were seen as optimal terrain for light, highly portable anti-tank weapons, and this supported the efficiency of such short-range weaponry. FDF Capt Martti Frick also popularised a doctrine that the short-range weaponry should be used also offensively, not just as self-defence, contrary to the doctrine of the German colonel Hermann Oehmichen during the World War II.[3]
The FDF committee for anti-tank weaponry pointed out that the Panzerfaust, Panzerschreck and Bazooka had been the most successful anti-tank weapons in the World War II. The American Bazooka was seen as the most successful and advanced of the three.[3] FDF however had already developed venturi effect recoil dampers to the Panzerschreck during the WWII to lengthen its range, and they were planned for the Panzerfaust as well, which were also tested in the early 1950s.[3]Rocket-propelled grenades (which have an in-flight burning rocket projectile) were however viewed with prejudice, as the Panzerschreck was considered by FDF as having a poor accuracy, which was attributed to its rocket projectile.[3]
When the proper development for a multi-use launcher which used the recoilless gun principle of the Panzerfaust began, it was led by two different teams, FDF HQ firearms division development team and privately, by a private company Raikka Oy. The FDF development team was led by MSc, Capt Esko Puronto and the Raikka Oy team by Helsinki University professor of ballistics, DSc, Lt Col Ilmari Liikkanen.[3] Both designs were recoilless guns; the FDF design was based on a venturi effect recoil damper, while the Raikka design was based on an ejected counter-mass to make the launcher recoilless.[3]
The Raikka design was criticised by the FDF development team as obsolete and not used by other countries, as well as making the launch tube wear out quicker. The leader of the FDF team Puronto commented, that he "would support the solution offered by Liikkanen, if it had more pros than cons".[3] The Raikka design would have had been safer to use in fortified positions as well as indoors due to the minimal backblast, but minimising the backblast was not a primary concern. The counter-mass made the projectiles of the Raikka design also heavier than those of the 55 S 55.[3]
The 55 S 55 launch tube was developed solely by the FDF development team, but the recoil damper was designed by Kaarlo Sarkimo of the Ammus Oy.[3]
FDF chose the FDF development team design based on technological principles, as well as being in possession of the intellectual property. Ammus Oy licensed the recoil damper to FDF for production to FDF use, so FDF could manufacture the weapon without any limitations.[3] Commercial designs (such as the Raikka weapon) were seen problematic, as they couldn't be manufactured by FDF without negotiations by the intellectual property holder.[3]
FDF was initially very satisfied with the 55 S 55, and in the 1960s it was considered to be at the pinnacle of the development of anti-tank weapons worldwide.[3] However, over time the opinion on the 55 S 55 grew more negative as the weapon grew dated, and FDF could address some design flaws and manufacturing decisions which compromised the durability and safety of the weapon;[3] however during the assessment of the criteria for the project, Capt Frick had viewed that that manufacturing and design should cut short some aspects to bring down the manufacturing costs, so the launchers could be widely distributed.[3] The 55 S 55 was also considered too heavy in the later reviews.[3]
Simplified backup sights were planned to be included in the design, but were never incorporated in the produced launchers.[3]
The 55 S 55 was manufactured until the 1970s, and manufacturing ceased after the FDF quota for the launchers had been fulfilled; over 10 000 launchers had been made. It was eventually removed from FDF service in the 1990s.[1]
Design
Sight picture of the 55 S 55 NE sight.
The main principle in the 55 S 55 is that of a smoothbore recoilless gun with a venturi effect recoil damper.[3] It is developed based on the Panzerfaust,[3] and is similar to the Swedish (Carl Gustaf 8.4cm recoilless rifle), German (Panzerfaust 2) and Soviet (RPG-2) designs of the time, though its design was not influenced by them.[3] Like the Carl Gustaf, the projectiles of the 55 S 55 aren't rocket propelled; all of the forward momentum is gained from the propellant charge, which burns immediately at the launch.[3]
The 89 millimetre HEAT grenade weighs 2.3kg, and is capable of penetrating 300 millimetres of RHA[2] +/- 40 millimetres. The fuse is able to function at as small as a 20 degree angle of impact.[2] The longest recommendable distance for stationary armour targets is 300 metres and to moving targets 200 metres.[2] 55 millimetre fragmentation[2] and incendiary WP grenades[4] as well as illumination rounds[4] and 55 millimetre solid training ammunition[2] were also available. The fragmentation and training ammunition weighed also 2.3kg, and had the same 160m/s muzzle velocity as the HEAT grenade.[2] If capped, the fragmentation grenade can penetrate obstacles such as light doors, bushes and windows before exploding. These can be shot up to 700 metres against stationary targets.[2] A rifle calibre practice barrel chambered in 7.62×54mmR could be installed inside the launching tube.
The backblast from the 55 S 55 is lethal or highly dangerous up to 7 metres; gravel, small rocks and other small objects could be propelled up to 15 metres behind. The gunner should have at least two metre clearance behind, so the backblast wouldn't be deflected back to the shooter; shooting from an enclosure was forbidden.[2]
Different types of ammunition for the 55 S 55.
The sights are optical; three types of different optical sights exist (Kr, D and NE), of which two (Kr and D) share the same reticle; the NE sight has a stadiametric rangefinder reticle.[2] There's provision for illuminating the reticle and the stadia marks in the NE sight.
The 55 S 55 was the standard anti-tank weapon of the Finnish Army from the late 1950s but has been phased out since the 1980s giving way to M72 LAW and Apilas. The weapon was operated by a two-man team, loader and the gunner.[2]
The main disadvantage of the weapon was low muzzle velocity resulting in an arched trajectory. This exposed the grenade to wind conditions and branches in covered terrain. Also the smoke and noise when firing could reveal the location making the user(s) a target. The weapon had a tendency to nod on launch requiring careful handling.
A rocket-propelled grenade (RPG) is a shoulder-fired rocket weapon that launches rockets equipped with an explosive warhead. Most RPGs can be carried by an individual soldier, and are frequently used as anti-tank weapons. These warheads are affixed to a rocket motor which propels the RPG towards the target and they are stabilized in flight with fins. Some types of RPG are reloadable with new rocket-propelled grenades, while others are single-use. RPGs are generally loaded from the front.
A recoilless rifle (rifled), recoilless launcher (smoothbore), or simply recoilless gun, sometimes abbreviated to "RR" or "RCL" is a type of lightweight artillery system or man-portable launcher that is designed to eject some form of countermass such as propellant gas from the rear of the weapon at the moment of firing, creating forward thrust that counteracts most of the weapon's recoil. This allows for the elimination of much of the heavy and bulky recoil-counteracting equipment of a conventional cannon as well as a thinner-walled barrel, and thus the launch of a relatively large projectile from a platform that would not be capable of handling the weight or recoil of a conventional gun of the same size. Technically, only devices that use spin-stabilized projectiles fired from a rifled barrel are recoilless rifles, while smoothbore variants are recoilless guns. This distinction is often lost, and both are often called recoilless rifles.
High-explosive anti-tank (HEAT) is the effect of a shaped charge explosive that uses the Munroe effect to penetrate heavy armor. The warhead functions by having an explosive charge collapse a metal liner inside the warhead into a high-velocity shaped charge jet; this is capable of penetrating armor steel to a depth of seven or more times the diameter of the charge. The shaped charge jet armor penetration effect is purely kinetic in nature; the round has no explosive or incendiary effect on the armor.
The Panzerfaust was a development family of single-shot man-portable anti-tank systems developed by Nazi Germany during World War II. The weapons were the first single-use light anti-tank weapons based on a pre-loaded disposable launch tube, a weapon configuration which is still used today.
Panzerschreck was the popular name for the Raketenpanzerbüchse 54, an 88 mm reusable anti-tank rocket launcher developed by Nazi Germany in World War II. Another earlier, official name was Ofenrohr.
Shoulder-fired missile, shoulder-launched missile or man-portable missile, among other variants, are common slang-terms to describe high-caliber shoulder-mounted weapons systems – that is: weapons firing large heavy projectiles ("missiles"), typically using the backblast principle, which are small enough to be carried by a single person and fired while held on one's shoulder. The word "missile" in this context is used in its original broad sense of a heavy projectile, and encompasses all shells and rockets, guided or unguided. A more formal variant is simply shoulder-fired weapons system and the like.
The Mk 153 Shoulder-Launched Multipurpose Assault Weapon (SMAW) is a smoothbore shoulder-fired rocket launcher. It is a portable assault weapon and has a secondary anti-armor ability. Developed from the B-300, it was introduced to the United States Armed Forces in 1984. It has a maximum effective range of 500 metres (550 yd) against a tank-sized target.
The Carl Gustaf 8.4 cm recoilless rifle is a Swedish-developed 84 mm (3.3 in) caliber shoulder-fired recoilless rifle, initially developed by the Royal Swedish Army Materiel Administration during the second half of the 1940s as a crew-served man-portable infantry support gun for close-range multi-role anti-armour, anti-personnel, battlefield illumination, smoke screening and marking fire, which has seen great export success around the globe and continues to be a popular multi-purpose support weapon in use by many nations. The Carl Gustaf 84 mm recoilless rifle is a lightweight, low-cost weapon that uses a wide range of ammunition, which makes it extremely flexible and suitable for a wide variety of roles.
The Panzerfaust 3 is a modern semi-disposable recoilless anti-tank weapon, which was developed between 1978 and 1985 and first entered service with the Bundeswehr in 1987. It was first ordered in 1973 to provide West German infantry with an effective weapon against contemporary Soviet armor, thereby replacing West Germany's aging PzF 44 Light Lanze launchers and the heavy Carl Gustaf 84 mm anti-tank recoilless rifle manufactured in Sweden.
The Splitterring was a fragmentation sleeve for the M24 and M43 stick grenades, developed by the Heer in 1942. German stick grenades had only a thin steel casing surrounding the explosive charge, which relied principally on blast for effect; the addition of a Splitterring gave it greatly increased anti-personnel fragmentation ability.
The Type 98 (PF-98) is a 120mm unguided anti-tank rocket system developed by Norinco for the People's Liberation Army as a successor to the Type 65 and Type 78 recoilless guns. It is also known by its nickname, "Queen Bee". It can be equipped with a firing control system which can calculate and adjust for projectile drop before the rocket fires.
The RPG-43 was a high-explosive anti-tank (HEAT) shaped charge hand grenade used by the Soviet Union during World War II. It entered service in 1943, replacing the earlier models RPG-40 and RPG-41; the RPG-40 used a simpler high explosive (HE) warhead. The RPG-43 had a penetration of around 75 millimetres (3.0 in) of rolled homogeneous armour at a 90 degree angle. Later in the war, it was improved and became the RPG-6.
The RPG-1 was a Soviet lightweight anti-tank warfare rocket-propelled grenade (RPG) equipped with a shaped charge warhead. The design was inspired by similar weapons being introduced by the US and Germany in the late-World War II period. Work on the design began in 1944 and continued until 1948, but it was not put into production, as the RPG-2 was selected for this role instead. The RPG-1 introduced the basic physical and mechanical layout that was also used on the RPG-2 and the far more famous and ubiquitous RPG-7.
The 8.8 cm Raketenwerfer 43 Puppchen was an 88 mm calibre reusable anti-tank rocket launcher developed by Nazi Germany during World War II.
The PzF 44, was a West German portable recoilless shoulder-fired anti-tank rocket launcher with a barrel-caliber of 44 mm (1.7 in). It was the spiritual successor to the Panzerfaust from World War II and served with the West German Army from the early 1960s to the early 1990s, when it was replaced by the Panzerfaust 3 semi-disposable launcher.
The Miniman is a disposable single-shot 74-mm unguided anti-tank smooth bore recoilless weapon, designed in Sweden by Försvarets Fabriksverk (FFV) and became operational in 1968.
The high–low system is a design of cannon and anti-tank warfare launcher using a smaller high-pressure chamber to store propellant. It allows a much larger projectile to be launched without the heavy equipment usually needed for large caliber weapons. When the propellant is ignited, the higher pressure gases are bled out through vents at reduced pressure to a much larger low pressure chamber to push a projectile forward. The high-low system allows the weight of the weapon and its ammunition to be reduced significantly. Production cost and time are drastically lower than for standard cannon or other small-arm weapon systems firing a projectile of the same size and weight. It has a far more efficient use of the propellant, unlike earlier recoilless weapons, where most of the propellant is expended to the rear of the weapon to counter the recoil of the projectile being fired.
Man-portable anti-tank systems are traditionally portable shoulder-launched projectile systems firing heavy shell-type projectiles, typically designed to combat protected targets, such as armoured vehicles, field fortifications and at times even low-flying aircraft.
The Tampella 100 PSTK is a Finnish towed 100 mm anti-tank gun, designed in the 1980s by Tampella. It was designed for commonality with the D-10T tank gun, in use by the Finnish Defence Forces in the T-54 and T-55 tanks, as well as the 100 56 TK coastal artillery piece. However, due to multitude of reasons it never went into serial production.
References
1 2 3 4 "Konepajaosasto 1950—1980". lonnstrominmuseot.fi (in Finnish). Teresia ja Rafael Lönnströmin Säätiö. Archived from the original on 13 May 2019. Retrieved 31 January 2020.
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