The cannon was developed within the research framework "Regina". The program's goal was to create a 155 mm long-range artillery piece for the Polish Army that would serve as a division levelasset. It was decided, that instead of buying a licence for a complete vehicle, only a licence for a modern L/52 gun and turret would be bought, and they would be mounted on domestically developed chassis. In 1997 there was announced a contest for an artillery part. The British AS-90M was a winner, and in 1999 its technology was transferred to Huta Stalowa Wola factory. The chassis UPG-NG was developed in Poland by OBRUM in Gliwice, from a chassis SPG-1M, utilizing parts unified with the PT-91 Twardy tank. The first prototype was completed in 2001, the second - next year. The first two examples of the howitzer are fitted with turret systems supplied by BAE Systems. It was planned to complete the first squadron in 2008, but the program was delayed due to financial reasons, and only in 2008 Polish Army ordered the first introduction batch of the squadron module, completed in 2012. It covers eight guns, command vehicles, plus ammunition vehicles and repair vehicles for the armament and electronics, as well as the fire control system etc. In the introductory and series products original British guns were replaced by those supplied by Nexter. Trial firing of another gun supplied by the maker is realized every month until the end of the year. These are realized at the Dynamic Trial Center of the WITU in Stalowa Wola. The first firing of the third complete Krab was carried out on 29 July 2011. Concentration of fire was tested, among others. As of 2012 two prototypes and eight initial units have been built by Huta Stalowa Wola. In 2012-2013 eight new examples were used for tests conducted by the Polish Army as a part of the battery command module "Regina". Eventually, on 17 December 2014 the Polish Ministry of Defense announced the deal worth US$320M with Korean Samsung Techwin to purchase 120 K9 Thunder chassis, with first 24 to be delivered in 2017 and 96 to be built under license in Poland in 2018-2022. Poland also evaluated the Turkish built T-155 Firtina chassis of the same origin. The original Polish OBRUM's UPG-NG chassis build by BUMAR equipped with an S-12U engine and other elements from the PT-91 Twardy used in eight initial production howitzers was abandoned due to cracks in its structure and ceased production of S-12U engines. The first K9 chassis was shipped to Poland for testing and integration in June 2015. The prototype was rolled out on 24 August 2015. It went through type acceptance testing in October 2015. The type examination ended successfully in April 2016 allowing serial production. On 7 April 2016 Ministry of National Defence and manufacturer concluded the research and development phase. On 28 April 2016 during Polish Prime Minister visit in Stalowa Wola first two serial examples were handed over to Polish Army. They joined eight initial production examples in Artillery Training Center in Toruń. They were used to elaborate operational norms for combat units. During handover ceremony on 18 November 2016 nine Krabs were accepted in the present of Polish Minister of National Defence, while seven more were in acceptance testing phase. Eight original turrets on UPG chassis are scheduled to be upgraded with K9 chassis after first batch of 16 guns is delivered by the end of 2016. The deal for following 96 units was signed on December 14, 2016, raising total order to 120 Krabs for five regiments. Each of the planned five squadrons of Krabs is going to be equipped with 24 howitzers. The first unit to receive 24 Krabs by 2017 will be 11th Masurian Artillery Regiment in Węgorzewo. The development program of advanced, smart 155 mm ammunition is started and is expected to conclude in 2017.
