Bofors 57 mm Mk.1 gun

While the 57 mm cannon may not seem as powerful as larger naval guns, such as the OTO Melara 76 mm, some of its performances are comparable; given its rate of fire and amount of explosive per shell, the Bofors gun actually achieves a higher amount of "explosive fired per second" than the 76 mm. Although the Swedish Navy has been the primary user of the gun, it has been exported widely by Bofors Defence for use by the navies of Brunei, Canada, Croatia, Finland, Indonesia, Ireland, Malaysia, Mexico, Montenegro, Singapore, Thailand, and the United States.

• Name — Bofors 57 mm Naval Automatic Gun L/70 • Origin — Sweden • Type — Naval artillery • Is Ranged — yes • Is Artillery — yes • Service — 1971–present • Used By — See users • Designer — Bofors Defence • Design Date — * Mark 1: 1970 • Mark 2: 1981 • Mark 3: 1995 • Manufacturer — * Bofors Defence (1970–2000) • United Defense (2000–2005) • BAE Systems AB (2005 onwards) • Production Date — * Mark 1: 1970 • Mark 2: 1985 • Mark 3: 2000 • Variants — See variants • Weight — Mark 3: 14000 kg (weight including 1,000 rounds onboard, each weighing 6.5 kg per complete round) • Part Length — * Bore length: 3990 mm • Without flash hider: 4045 mm • With flash hider: 4345 mm • Cartridge — 57 × 438 mm R (m/70) 6.1 kg complete round 2.4 kg pre-fragmented shell • Caliber — 57 mm/70 caliber • Barrels — Single barrel (progressive RH parabolic twist, 24 grooves) • Action — Electronic firing • Rate — * Mark 1: 200 rounds/min • Mark 2: 220 rounds/min • Mark 3: 220 rounds/min • Velocity — 1035 m/s (HE round) • Range — 8500 m (HE round) • Max Range — 17000 m (HE round at 45°) • Feed — Magazine: • Mark 1: 40 ready rounds, 128 rounds in ready racks in mount • Mark 2: 120 ready rounds, up to 40 rounds in dual hoists • Mark 3: 120 ready rounds, up to 40 rounds in dual hoists, 1,000 rounds in mounting • Sights — Gyro-stabilized in local control. • Elevation — * Mark 1: −10°/+78° (40°/s) • Mark 2: −10°/+75° (40°/s) • Mark 3: −10°/+77° (44°/s) • Traverse — Full 360°: • Mark 1: 55°/s • Mark 2: 55°/s • Mark 3: 57°/s

The gun is formally known under a variety of names around the globe. Internally at Bofors (now BAE Systems AB) it usually goes under names incorporating the Bofors term 'SAK', an acronym for 'SjöAutomatKanon', meaning "Sea Automatic Cannon" (literal) or "Naval Automatic Gun" (formal). Some examples being: 57 mm SAK 70 (57 mm sjöautomatkanon L/70) and SAK 57 Mk1, SAK 57 Mk2, SAK 57 Mk3, etc. Not to be confused with the Bofors 57 mm Naval Automatic Gun L/60 which has gone under similar names like 57 mm SAK 60 (57 mm sjöautomatkanon L/60). BAE Systems has also stated on their website that the current generation of the weapon, the mark 3, is simply known as the 57Mk3 internally as of 2011.

The Bofors 40 mm L/60 anti air gun (1.6 inch) was one of the most popular naval anti-aircraft guns during World War II, used long after the war in a variety of roles. However, as jet aircraft became more prevalent in the post-war era, it was clear the gun did not have the rate of fire needed to effectively deal with these threats. Flying at speeds close to 1000 km/h, a jet aircraft flew through the effective range of the Bofors 40 mm gun in too short a time for the gun to fire enough rounds to ensure a hit. Bofors' engineers considered two solutions to the problem. One was to greatly increase the firing speed of the 40 while also incorporating any minor changes that would improve its range. This produced the 40 mm L/70, which remains popular to this day. The other was to design a larger weapon with much greater effective range and a larger explosive load that offset a lower firing rate. This eventually resulted in the single-barreled Bofors 57 mm Automatic A.A. Gun L/60 and twin-barreled Bofors 57 mm Naval Automatic Gun L/60 in 1950. The 57 mm L/60 systems were however far from ideal; they had a low rate of fire and were very big and heavy, especially the twin-barrel system. Due to the ever-improving performance of jet aircraft, a new and improved base design was needed by the late 1960s. The focus of the new design was to increase velocity, range and firing rate. This design became the 57 mm Naval Automatic Gun L/70.

The baseline version of the new gun, later known as the Mark 1, used a cartridge with the same case-length as the cartridge on the 57 mm Naval Automatic Gun L/60 (57 mm x 438 mm) but with a new shape and propellant, giving it an increased velocity of 1025 m/s, compared to 890 m/s on the L/60 cartridge. Fire rate was also higher on the L/70 design: 200 rounds per minute, compared to 130 rounds per minute per barrel on the 57 mm L/60-design. The Mark 1 gun mount featured a 40-round magazine and a further 128 rounds were stowed inside the Mark 1 turret. Aiming operation was performed by a new electro-hydraulic system for rapid training and elevation. • Illustration — Bofors 57/70 Mark 1 firing from a Swedish. • Illustration — Bofors 57/70 Mark 1 on a Swedish Norrköping-class missile boat. • Illustration — Bofors 57/70 Mark 1 on a Swedish Norrköping-class missile boat. • Illustration — Bofors 57/70 Mark 1 on a Swedish Norrköping-class missile boat. The 57 mm L/70 Mark 1 was introduced into the Swedish Navy in 1971 as the 57 mm automatpjäs 7101 (57 mm apj 7101) on the fast attack craft, also known as the Spica-II-class (not to be confused with the (Spica-I)). It featured two ammunition hoists. A second variant designated 57 mm apj 7102 was introduced in 1972 on the patrol boat HSwMS Jägaren. It was similar to the 7101 but featured only a single ammunition hoist. Besides Sweden, the Mark 1 also saw adoption with Finland, Malaysia, Norway, Indonesia, Singapore and (the former) Yugoslavia.

The Mark 2 was an improved variant of the gun designed in 1981. It featured a slightly higher rate of fire of 220 rounds per minute, had a lighter weight, and utilized a new servo drive/servomechanism system which compensates for barrel oscillations during firing, increasing the hit probability. According to Bofors, the new servo system allowed the Mark 2 to be both accurate and agile enough for use against sea skimming anti-ship missiles and that it could put more explosives into a surface target within a thirty-second window than any naval gun with a calibre smaller than 100 mm. The Mark 2 gun is fitted with a 40-round ready-use gun-magazine with four vertical 10-round compartments. There are also cassettes inside the mounting for 80 more ready to use rounds (120 rounds total in the mounting). Ammunition is hoisted manually into the mounting using two manual-hoists which feeds from the ammunition-room below the mounting. Bofors claims that with 120 ready rounds the system can sufficiently engage 1 to 2 surface targets and 4 sea skimming missiles. To remove weight from the design, the Mark 2 variant omitted the water-cooling used on the Mark 1. This meant a lighter barrel and gun mount. According to Bofors, water-cooling was not needed for the modern missions the Mark 2 was used for. Bofors even recommended that water-cooling be removed from older mountings. The Mark 2 gun barrel was also forged from monobloc steel to help with heat-wear from the lack of water-cooling. The Mark 2 mounting originally also had room for a gun operator, however, the compartment was too narrow for practicality and the wind-shield proved to be a source for radar-reflections, and was quickly replaced by a TV-camera. • Illustration — Bofors 57/70 Mark 2 firing from a Canadian. • Illustration — Bofors 57/70 Mark 2 on the Malaysian frigate Jebat. • Illustration — Bofors 57/70 Mark 2 on the Malaysian frigate Jebat. • Illustration — Bofors 57/70 Mark 2 on the Malaysian frigate Jebat. • Illustration — Bofors 57/70 Mark 2 on the Malaysian frigate Lekiu. The 57 mm L/70 Mark 2 was introduced into the Swedish Navy in 1985 as the 57 mm automatpjäs 7103 (57 mm apj 7103) on the —HSwMS Stockholm (sister ship HSwMS Malmö was built in 1984 but armed with the older Mk1, subsequently retrofitted with the Mk2 in 2009). An improved version designated 57 mm automatpjäs 7103B (57 mm apj 7103B) was introduced in 1990 on the. Beyond Sweden the Mark 2 also saw adoption by Canada and four other navies. Bofors has manufactured a total of about 25 Bofors 57 mm L/70 Mark 2 guns.

The latest development of the gun is the Mark 3, designed in 1995 for use on the then planned Visby-class corvette. The Mark 3 system has kept the same rate of fire and ammunition capacity as the previous Mark 2 system but has added many features to make it a modern system. Some of the primary changes includes: the ability to use Bofors 3P all-target programmable ammunition, the addition of a small muzzle velocity radar housed in a radome externally above the gun barrel for measuring the muzzle velocity of the departing projectiles for fire-control purposes, usually but not necessarily with the new Bofors 57 mm 3P ammunition, the ability to instantly change ammunition types by the use of a dual-feed system, another 1,000 rounds stowed in the standby rack beneath deck, as well as an improved fire control system. The Mark 3 system can also be operated/fired manually without the FC system using a joystick and video camera (mounted on the gun). The camera is fitted as standard. For the Visby-class corvette Bofors also developed a new optional low radar profile (also known as low radar cross-section, or RCS) stealth mounting (also known as a cupola), which allows the gun to be hidden from radar and plain sight when not in use. The stealth mount/cupola is made of carbon-fibre-reinforced polymer and has a very distinctive angular, low signature. • Illustration — Bofors 57/70 Mark 3 (Mk 110) with standard mount firing from an American Freedom-class littoral combat ship. • Illustration — Bofors 57/70 Mark 3 with standard mount on Finnish missile boat Hamina-class missile boat. • Illustration — Bofors 57/70 Mark 3 with stealth mount in "transport mode" aboard a Visby-class corvette. • Illustration — Bofors 57/70 Mark 3 with stealth mount in "fire mode" aboard a Visby-class corvette. The Bofors 57 mm SAK L/70 Mk3 was introduced into service with the —fitted on Visby in the year 2000. It has since also been adopted by a variety of nations, such as Finland and the United States. In American service, the United States Navy has designated the Mark 3 as the Mark 110 Mod 0 57mm gun. According to a BAE Systems press release dated 1 August 2005, the Mark 110 would be manufactured at the BAE Systems facility in Louisville, Kentucky. BAE Systems has been awarded a contract by General Dynamics to provide two additional Mk110 Naval Gun Systems for the Independence variant of the US Navy's (USN's) Littoral Combat Ship (LCS).

• Illustration — Sailors load ammunition aboard Gabrielle Giffords Ammunition for the Bofors 57 mm gun is produced by BAE Systems, Sako Limited in Finland, SME Ordnance in Malaysia and Nammo in Norway. In 2006, BAE Systems AB began to offer the Bofors 57 mm 3P all-target programmable ammunition, this allows three proximity fuzing modes as well as settings for time, impact, and armor-piercing functions. This increases the flexibility and effectiveness of the gun system, which has further reduced the reaction time of the gun and it is possible to choose ammunition mode at the moment of firing, giving it the ability to switch rapidly between surface targets, air targets, and ground targets. In April 2015, BAE Systems unveiled a new round for the Mk 110 in the design stage called the Mk 295 Mod 1 Ordnance for Rapid Kill of Attack Craft (ORKA), made to achieve one shot kills of surface and air threats. Answering a U.S. Navy requirement for increasing the accuracy and efficiency of naval rounds, the ORKA leverages technology BAE Systems developed for larger 127 mm and 155 mm guided rounds, using a 4-canard actuation systems to guide the round. It is fitted with a multi-mode imaging semi-active seeker that can be guided through laser designation or autonomous targeting by downloading image of the target prior to firing; ORKA retains the 3P multiple fuzing modes. In December 2015, the U.S. Navy revealed they were working on developing a guided 57 mm round for its Mk 110 guns on the Littoral Combat Ship and other Navy and Coast Guard ships. Northrop Grumman was awarded a contract to develop a self-guided 57 mm shell for the Mk 110 in October 2023. On 22 August 2017 L3 Mustang Technology (part of L3Harris Technologies) announced the completion of the Critical Design Review (CDR) phase for the U.S. Navy's MK 332 Mod 0 High-Explosive, 4-Bolt Guided (HE-4G) projectile. The round was developed from the Advanced Low-Cost Munitions Ordnance (ALaMO) program. It is intended for use on the LCS and the new fast Frigate, and the US Coast Guard's Legend and Heritage class cutters.

• Bofors 57 mm SAK L/70 Mk1:Baseline version from 1970. 200 rounds per minute rate of fire, water-cooled. • 57 mm automatpjäs 7101 (57 mm apj 7101) – Swedish navy version with two ammunition hoists. • 57 mm automatpjäs 7102 (57 mm apj 7102) – Swedish navy version with one ammunition hoist. • Bofors 57 mm SAK L/70 Mk2:Improved version from 1981. 220 rounds per minute rate of fire, lighter weight, new servo system, no water-cooling. • 57 mm automatpjäs 7103 (57 mm apj 7103) – Swedish navy version for the Stockholm-class corvette. • 57 mm automatpjäs 7103B (57 mm apj 7103B) – Swedish navy improved version for the Göteborg-class corvette. • 57 mm allmålskanon Mk2 – Post 2001 designation for the 57 mm apj 7103A and 7103B. • Bofors 57 mm SAK L/70 Mk3:Improved version from 1996 based on the Mk2. Ability to use programmable ammunition. • 57 mm allmålskanon Mk3 – Swedish navy stealth version for the Visby-class corvette. • 57 mm allmålskanon Mk3B – Swedish navy version. 57 mm allmålskanon Mk2 modified to be able to fire Mk3 programmable ammunition. • 57 mm Mark 110 Mod 0 Naval Gun System – Slightly modified Mark 3 offered for use by the United States Coast Guard in 2004 and the United States Navy in 2006. The Bofors 57 mm programmable 3P ammunition is designated as Mark 295 Mod 0 in US service.

• Illustration — Singaporean RSS Sea Dragon with its Bofors 57 mm L/70 Mk1. •: • Madhumati class • Meghna class •: • * • fast attack craft •: • * • * •: • Bung Hatta (interim gun, to be replaced by OTO Melara 76) • (modified version of the South Korean Navy's Bae Ku class) • (retired) * • Eithne (retired 2022) •: • * • Perdana class • * • * •: • fast attack craft •: • Sea Wolf class (Lurssen TNC 45) (retired) * • Swedish designations: • 57 mm automatpjäs 7101 (57 mm apj 7101) • 57 mm automatpjäs 7102 (57 mm apj 7102) • Swedish usage: • (retired) • (retired) • (retired) • Carlskrona (guns replaced with other weapons) * • Prabbrorapak class (derivative of Singapore's Sea Wolf class, which was based on the Lurssen TNC 45) (retired) •: • Begleitpanzer 57 AIFSV prototype (retired)

• Illustration — Malaysian frigate Jebat (right) during the Royal Australian Navy International Fleet Review 2013 with its Bofors 57 mm L/70 Mk2. •: • (Pre HCM/FELEX) (replaced with Mark 3 gun) •: • Singa class (Lürssen FPB 57 Nav II, Fast Attack Craft - Torpedo) • Pandrong class (Lürssen FPB 57 Nav IV, Fast Attack Craft - Missile/Fast Patrol Boat) • Todak class (Lürssen FPB 57 Nav V, Fast Attack Craft - Missile/Fast Patrol Boat) •: • * * • Swedish designations: • 57 mm automatpjäs 7103 (57 mm apj 7103), later changed to 57 mm allmålspjäs Mk2 • 57 mm automatpjäs 7103B (57 mm apj 7103B), later changed to 57 mm allmålspjäs Mk2 • Swedish usage: • * • *

• Illustration — Bofors 57 mm Mk3 on Finnish missile boat Hanko • Illustration — Freedom firing its 57 mm Mk 110 Mod 0 gun. •: • * •: • (Post HCM/FELEX Refit / 2x MK3 operational prior to Halifax Class Modernization (HCM) refit) •: • * • (under construction) •: • Potsdam class •: • (The last four ship of the class) •: • (under construction) •: • * • * • Reformador class • * * • Swedish designations: • 57 mm allmålspjäs Mk3 • 57 mm allmålspjäs Mk3B • Swedish usage: • * • * • * •: • * • United Kingdom • Type 31 (under construction) * • US designation: • Mk 110 57mm gun • US usage: • Legend class • Heritage class (under construction) • * • * • (under construction)