K9 Thunder
The K9 Thunder is a South Korean 155 mm self-propelled howitzer designed and developed by the Agency for Defense Development and private corporations including Samsung Aerospace Industries, Kia Heavy Industry, Dongmyeong Heavy Industries, and Poongsan Corporation for the Republic of Korea Armed Forces, and is now manufactured by Hanwha Aerospace. K9 howitzers operate in groups with the K10 ammunition resupply vehicle variant.
The entire K9 fleet operated by the ROK Armed Forces is now undergoing upgrades to K9A1, and a further upgrade variant K9A2 is being tested for production. As of 2022, the K9 series has had a 52% share of the global self-propelled howitzer market, including wheeled vehicles, since the year 2000.
Development
In the 1980s, the ROK Armed Forces embarked on the development of a new artillery system to contest North Korean equipment. The armed forces operated M107 self-propelled guns and K55 self-propelled howitzers. However, they had shorter firing ranges compared to M-1978 Koksan and were outnumbered by various North Korean artillery. With the success in designing and manufacturing the KH178 105 mm and KH179 155 mm towed howitzers, and experience gained by license producing the K55, the Ministry of Defense ordered the development of a new system that would have a longer firing range, faster firing rate, and high mobility. The development started in 1989 and was led by the Agency for Defense Development and Samsung Aerospace Industries.Since 1983, the ADD researchers had been collecting and analyzing data for future artillery. They saw that burst fire and quick relocation would become the dominant factor in artillery battles and built an automatic loading system for testing in 1984. In 1987, the ADD offered an upgrade plan to the existing K55 inspired by the United States' M109 Howitzer Improvement Program, but was rejected by the Republic of Korea Army in 1988. As a result, and at the beginning of K9 development, the ADD was determined to create a new weapon system and worked on a conceptual model until 1991. Early concepts requested by the military included river crossing capability and the installation of M61 Vulcan as an anti-air weapon, which were later removed due to being unnecessary for such a long-range weapon.
In 1989, the only design data the researchers could obtain at that time were the provisions of the four-nation ballistic agreements, namely the United States, the United Kingdom, Germany, and Italy, to secure the homogeneity of the ammunitions—the new 52 caliber gun fires a NATO standard ammunition at a speed of 945 m per second from chamber volume of 3,556 cm3. The first domestic design was prepared by extending and modifying the 155 mm 39 caliber gun used for the KH179. The first firing test was held in January 1992 but experienced many problems due to design errors.
In September 1990, a Korean developer visited the United Kingdom in search of turret design technology which was known to have been developed by British Vickers for AS-90. Vickers refused the technology transfer. Instead, the company offered the AS-90 for sale. The developer also visited Marconi, but the negotiations ended with an unsatisfactory result due to a high requested price. Therefore, developers pursued a domestic electrohydraulic driving system, using the experience in turret design and turret driving devices of the K1 MBT. The simulator was built in 1991.
The next year, researchers found that the disproportionate moment of the 52-caliber was twice of the K55. The balancing machine, which increased the capacity of the existing hydraulic balancing machine, did not sufficiently compensate for the imbalance moment value due to the change in the position of the armament. The driving force was very different depending on the driving angle. The same problem appeared in Germany's Panzerhaubitze 2000, which was under development. A joint research team from the ADD and Seoul National University of Science and Technology calculated an accurate theoretical model, and concluded that adjustment to system configuration was possible without major design changes.
Meanwhile, loud noise from hydraulic generators, which can cause hearing loss under long exposure, was also a problem. The engineers of the ADD and Dongmyeong Heavy Industries found that the noise was due to excessive shaking of hydraulic pressure, thus creating an experimental device using the principle of Helmholtz attenuators used in car mufflers. The noisy equipment became quieter and the hydraulic pulsation was significantly reduced. Overall, the domestic design showed driving precision of less than 1 mil in the standard error range.
In the winter of 1991, the ADD held talks with engineers from Samsung Aerospace Industries' special research institute. The ADD originally demanded that Samsung be in charge of system assembly only, as the company had no experience in developing its own tracked vehicle design despite having the experience in manufacturing K55 under license. The decision was overturned and the manufacture of the MTR was decided upon. Samsung worked with KAIST on suspension and Seoul National University & Pohang University of Science and Technology on mobility systems. The engine was co-developed with American AAI Corporation. The test of the MTR was finished in November 1992.
In April 1992, BMY Combat Systems invited members of the ADD for its first M109A6 Paladin release ceremony and expressed interest in participating in Korea's self-propelled howitzer program by upgrading the K55 to Paladin standard. In May, members of BMY Combat Systems and Teledyne Brown visited the ADD, and suggested co-development of a new howitzer based on the P-52, a 52-caliber Paladin variant. This proposal was rejected by Korean developers. Later, during a Data Exchange Agreement meeting, South Korea and the United States confirmed that the U.S. had no claim to any intellectual property rights of the howitzer, to avoid possible disputes in the future.
From 1992 to 1993, the developers explored and confirmed the required operational capability, such as the system suitability of major components and the possibility of reaching the maximum firing range of. An internal review predicted that the howitzer would achieve a localization rate of 107 out of 235 technologies by the late 1990s. Unsatisfied with the review, South Korea decided to continue developing main system, main gun, 155 mm ammunition, fire control system, structure, and autoloader; meanwhile, the engine, transmission, and INS were to be imported from foreign partners, and license produce hydropneumatic suspension to target 70% localization rate. The engineers faced the biggest challenges designing main gun and suspension due to lack of experience. While licensing the K55, its main gun was brought as a finished product and the suspension was produced from knowledge from the United States.
Based on a review of the required operational capability in October 1992, a firing rate of three shots within 15 seconds was chosen for economic feasibility. The rationale was that it is difficult for targets to be out of fatal range within 15 seconds after the first impact, and that the firing rate can be shortened depending on training level. If a firing rate of three shots in 10 seconds was demanded, it would have caused a huge increase in development costs as well as an unnecessary burden on researchers.
The development was delayed between March and August 1993 as a result of purge of Hanahoe, a private military club within the Republic of Korea Armed Forces, who aligned with military dictator Chun Doo-hwan, by president Kim Young-sam who was elected by democratic election. In addition, the army logistics department also refused to sign the letter of agreement for XK9 until a development plan for the maintenance elements is created. When the Joint Chiefs of Staff finalized the system development agreement in late August 1993, the Defense Ministry approved a prototype development plan in September and the president approved the project in early October.
Since domestically developed armor steel plates were applied for the first time, the researchers decided to produce and compare armor plates from both imported and domestic materials to reduce the risk. Meantime, Samsung began to train and employ master craftsman welders whose skills were verified by the U.S. Aberdeen Test Center. Armor plates went through a series of tests such as stress and ballistic impacts, and researchers verified that the domestic plate performed better than the imported plate.
The ADD saw that the HSU provides better mobility and crew comfort. At that time, the HSU caused problems with some equipment and it was yet to be fully verified for durability, igniting controversy internationally. Therefore, it was inevitable to introduce and localize a British Air-Log HSU that is used for the AS-90. However, when researchers applied the Air-Log HSU on the MTR and prototypes, they soon found that the HSU couldn't support heavier vehicles, thus failing the durability test. Since May 1997, engineers from the ADD and Dongmyeong Heavy Industries have spent a year on five redesigns and 11 durability tests. After the development of the new HSU, the design was exported back to Britain.
Developers changed the power pack for the MTR with the combination of an 850 hp engine from Detroit Diesel, which offered a smaller cooling system, and Allison Transmission's X1100 automatic transmission. This powertrain passed the tests on the MTR, but the engine failed on prototype vehicles due to low durability. The researchers looked for new engines from overseas. Perkins Engines and MTU Friedrichshafen showed interest in selling engines in August 1995. Perkins Engines offered the CV12 Condor, which was also used in the Challenger 2, but detuned to 1,000 hp. The price was slightly higher than that of Detroit Diesel; it was a relatively large 12-cylinder, which would require a design change on the chassis and there was a technical insufficiency of cooling devices. MTU's MT-881, though more expensive, offered a compact eight-cylinder with the same cutting-edge cooling system from the latest Euro Pack. The engine was also used for the PzH 2000 in Germany, and was undergoing trials in Germany and Canada. After examinations, the German design was chosen for the program, and was tested on an ATR for a year starting in September 1997.
In the spring of 1992, the test gun experienced a detonator breakage caused by a differential pressure, at which the pressure increases in the opposite direction of the shell. After many years of failures and updates, researchers decided to change the shape of the propellant in 1997. The tiny pellets of the U.S.-style propellant, which have seven holes similar to briquettes, were replaced with 19 holes by mimicking the German style without knowing the specification. After numerous tests, the gun achieved a range of below 53,000 psi in 1998.
A total of three prototypes were built and performed their first open trials in 1996. During the test, the prototypes succeeded in firing at distances of and six rounds per minute, but failed to fire three rounds in 15 seconds. In December 1997, one of the prototypes was damaged by fire, due to failing complete combustion, after testing 18 rounds in three minutes. One researcher was killed and two injured. The damaged prototype's internal system survived the fire, and was repaired for further use. The prototypes fired 4,100 rounds and underwent of mobility tests including extreme temperature conditions and various type of terrain such as ski courses during the winter season.
After firing 12,000 rounds and driving over 10 years, the development was finished in October 1998 with the achievement of an 87% localization rate. The contract for the Batch I of K9 artillery system was awarded to Samsung Aerospace Industries in December 1998. The produced vehicles were supposed to be delivered to the Republic of Korea Army. However, a 1999 naval battle between the two Koreas caused the delivery to be rerouted to the Republic of Korea Marine Corps. The first vehicle was rolled out in December 1999, and was given to the marines in Yeonpyeongdo.