Bofors 57 mm L/70 naval artillery gun

Naval artillery

The Bofors 57:mm L/70 naval guns are a series of dual-purpose naval guns designed and produced by the Swedish arms manufacturer AB Bofors (since March 2005 part of BAE Systems AB), designed in the late 1960s as a replacement design for the twin barreled Bofors 57 mm L/60 naval artillery gun. The gun is remotely controlled by a fire-control computer but can as a redundancy measure however also be operated manually by crew using instrument panels either on or in direct contact with the gun.

The gun has been upgraded and improved several times:

  • Mk1 – The baseline Mark 1 variant began production in 1970 and was initially used to equip smaller coastal patrol craft and fast attack craft.
  • Mk2 – The improved Mark 2 variant came in 1981 and drastically lowered the weight as well as introduced new servo stabilizers.
  • Mk3 – The improved Mark 3 variant came in 1995 and primarily features the ability to use programmable ammunition.

Although the Swedish Navy is 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.


Design and development

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 1,000 kilometres per hour (620:mph), 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 L70, 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 twin-barreled Bofors 57 mm L/60 naval artillery gun in 1950. The 57 mm L/60 however was far from ideal; it had a low rate of fire and was very big and heavy due to its twin barrel design. Bofors would quickly design a single barreled version of the 57 mm L/60 for both ground use and naval use. However, due to the ever improving Jet Age 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 L/70 naval artillery gun.

Mark 1

A 57 mm Mk 1 firing from a Swedish Norrköping-class missile boat

The baseline version of the new gun, later known as the Mark 1, was initially known as the 57 mm SAK 70, abbreviation for SjöAutomatKanon L/70 (Sea Automatic Cannon L/70), at Bofors. It used a cartridge with the same case-length as the cartridge on the 57 mm L/60 naval artillery gun (57 mm x 438 mm) but with a new shape and propellant, giving it an increased velocity of 1,025:m/s (3,360:ft/s), compared to 890:m/s (2,900:ft/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.

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 Norrköping-class missile boat fast attack craft, also known as the Spica-II-class (not to be confused with the Spica-class torpedo boat (Spica-I)). It featured two ammunition hoists. A second variant designated 57 mm apj 7102 was introduced in 1972 on the HMS Jägaren (V150) patrol boat. 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) Yugoslavi.

Mark 2

A 57 mm Mk 2 firing from a Canadian Halifax-class frigate frigate

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 (3.9:in).

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 wasn't needed for the modern missions the Mark 2 was used for. 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 turret 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.

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 Stockholm-class corvette—HSwMS Stockholm (sister ship HSwMS Malmö was built in 1984 but armed with the older Mk 1, subsequently retrofitted with the Mk 2 in 2009). An improved version designated 57 mm automatpjäs 7103B (57 mm apj 7103B) was introduced in 1990 on the Göteborg-class corvette. 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.

Mark 3

A 57 mm Mk 3 with standard cupola aboard a Hamina-class missile boatA 57 mm Mk 3 with stealth cupola aboard a Visby-class corvetteNote the prominent but small radome above the gun barrel which is used for measuring muzzle velocity of the departing projectile.

The latest development is the Mark 3, which was designed in 1995 but introduced into service with the Visby-class corvette—fitted on HSwMS:Visby in 2000. This new design retained the Mark 2 gun mount, rate of fire and ammunition capacity but can fire programmable ammunition, has another 1,000 rounds stowed in the standby rack beneath deck, and can change ammunition types instantly due to a dual-feed system. A small radome has been added above the gun barrel and is used for measuring the muzzle velocity of the departing projectiles for fire-control purposes, usually but not necessarily with the new Bofors 57:mm 3P all-target programmable ammunition. Also, a new optional low radar profile (also known as low radar cross-section, or RCS) stealth mounting was developed, which allows the gun to be hidden from radar and plain sight when not in use. The gun can also be operated/fired manually without the FC system using a joystick and video camera (mounted on the gun).

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).

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.


Sailors load ammunition aboard USS:Gabrielle Giffords

Ammunition for the Bofors 57:mm gun is produced by Bofors, 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.

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 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 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 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 7103A (57 mm apj 7103) – Swedish navy version for the Stockholm-class corvette.
  • 57 mm automatpjäs 7103A (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 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.


Mark 1 users

Singaporean RSS Sea Dragon with its Bofors 57 mm L/70 Mk 1 Swedish designations:
  • 57 mm automatpjäs 7101 (57 mm apj 7101)
  • 57 mm automatpjäs 7102 (57 mm apj 7102)
Swedish usage:

Mark 2 users

  • 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:

Mark 3 users

Bofors 57 mm Mk 3 on Finnish missile boat Hanko HSwMS Helsingborg firing her 57 mm allmålskanon Mk3 gun USS:Freedom firing its 57 mm Mk 110 Mod 0 gun.
  • Halifax class (Post HCM/FELEX Refit / 2x MK3 operational prior to Halifax Class Modernization (HCM) refit)
Swedish designations:
  • 57 mm allmålspjäs Mk3
  • 57 mm allmålspjäs Mk3B
Swedish usage: US designation:
  • Mk 110 57 mm gun
US usage:

See also


  1. ^ a b c d e f g h i "Sweden 57 mm/70 (2.25") SAK Marks 1, 2 and 3 / United States 57 mm/70 (2.25") Mark 110 Mod 0". NavWeaps.Com. 10 April 2008. Archived from the original on 3 September 2011. Retrieved 22 September 2011.
  2. ^ a b c d e f g h i j k l m n o p "Bofors automatic 57mm Dual-Purpose guns". Archived from the original on 2007-05-14. Retrieved 2021-10-22.
  3. ^ AMKAT, Ammunitionskatalog för marinen, Data och bilder, 1990 års utgåva (in Swedish). Sweden: Försvarets materielverk. 1990. pp.:39, 40, 43, 44.
  4. ^ a b c d e "57-mm Mk 110 Mod 0 Naval Gun System". BAE Systems. Archived from the original on 30 September 2009. Retrieved 22 September 2011.
  5. ^ "Navy League 2018: BAE Systems wins LCS naval gun contract". Jane's 360. Archived from the original on 2018-04-12. Retrieved 2018-04-11.
  6. ^ French Navy FTI Frigate: From 57mm to 127mm, Naval Gun System Choice Still Open Archived 2016-10-31 at the Wayback Machine -, 28 October 2016
  7. ^ "40 and 57 mm 3P ammunition". BAE Systems. 2006. Archived from the original on 26 September 2011. Retrieved 22 September 2011. updated page
  8. ^ BAE Systems Unveils the ORKA One Shot One Kill Round for 57mm Gun at Sea-Air-Space 2015 Archived 2015-09-22 at the Wayback Machine -, 14 April 2015
  9. ^ A Year Into Distributed Lethality, Navy Nears Fielding Improved Weapons, Deploying Surface Action Group Archived 2016-01-16 at the Wayback Machine -, 13 January 2016
  10. ^ "L3 Mustang Technology Passes U.S. Navy's Critical Design Review for Guided Projectile Program" (PDF). Archived from the original (PDF) on 28 August 2017. Retrieved 27 August 2017.
  11. ^ a b AMKAT, Gemensam Ammunitionskatalog, Data och bilder, 2001 års upplaga (in Swedish). Sweden: Försvarets materielverk. 2001. pp.:52, 53.
  12. ^ AMKAT, Gemensam Ammunitionskatalog, Data och bilder, 2011 års upplaga (in Swedish). Sweden: Försvarets materielverk. 2011. p.:95.
  13. ^ AMKAT, Gemensam Ammunitionskatalog, Data och bilder, 2014 års upplaga (in Swedish). Sweden: Försvarets materielverk. 2014. p.:95.
  14. ^ "FUZE 3P Programmable All-Target Ammunition | BAE Systems | International". Archived from the original on 2018-10-29.
  15. ^ a b c "Naval vessels as built by Lurssen GmbH". Archived from the original on 12 January 2014. Retrieved 26 January 2014.
  16. ^ "Mindef Accepts 2 Darussalam-Class Offshore Patrol Vessels" (Press release). Government of Brunei. Archived from the original on 2 April 2012. Retrieved 22 September 2011.
  17. ^ Frigate Equipment Life Extension
  18. ^ "German offshore patrol vessels getting BAE's 57mm naval guns".
  19. ^ Vavasseur, Xavier (2019-08-20). "BAE Systems 57mm Gun Systems Selected for Indonesia's New KCR-60M". Naval News. Retrieved 2021-09-17.
  20. ^ a b "57MM Naval Gun System". BAE. Archived from the original on 31 January 2017. Retrieved 18 January 2017.

External links


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