The Soko J-21 Jastreb is a Yugoslav military single-engine light attack jet aircraft of single-seat metal construction intended for close fire support and reconnaissance. It was produced based on the VTI project at the SOKO aircraft factory in Mostar from 1968 to 1977. The aircraft was created from the development project of the Soko G-2 Galeb military school jet, sharing many unified parts, which made production and maintenance cheaper.
Introduction
This was the second jet and the first fighter plane to be serially produced in Yugoslavia. Aerodynamicist Prof. Dr. Zlatko Rendulić led the project. The first test flight took place on July 19, 1965, and its introduction into service began on December 31, 1968. This marked the beginning of the gradual replacement of the F-84 Thunderjet, which was running low on resources and had been the main attack jet in the JRV until then. The Soko J-21 Jastreb first appeared at the Farnborough air show in 1968.
The Soko J-21 Jastreb could take off and land on grass runways. It was equipped with shooting weapons in the fuselage and unguided bombs and rockets on underwing mounts, enabling ground assault-combat operations. It could also operate alongside light aircraft such as helicopters and piston planes. The aircraft was produced in four variants. Aside from the standard J-21 (attacker) and IJ-21 (reconnaissance), the most significant variant was the J-1L, intended for export to Zambia and Libya. A total of 224 examples were manufactured, with 175 Jastrebs serving in the official capacity in the JRV, while the remaining units were export batches, which achieved considerable business success.
Development
The technology for producing Yugoslavia’s first subsonic jet aircraft was obtained through cooperation with the United Kingdom, which involved purchasing a license for the Armstrong Siddeley Viper turbojet engine and additional equipment like the Foland seat. This collaboration marked a significant technological advancement for Yugoslavia, with Mostar and SR BiH becoming hubs for one of the most advanced technologies in the country.
In contrast to the Soko G-2 Galeb, the J-21 Jastreb had a reinforced structure to accommodate higher payload capacity. It was also equipped with a slightly more powerful turbojet engine, designated Mk 521, providing a thrust of 1,333.7 daN. Some sources suggest that the Jastreb served as a transitional solution until the implementation of the classified military project “JUROM,” which focused on developing a new twin-engine attack jet called the J-22 Orao in collaboration between SFR Yugoslavia and the Republic of Romania during the 1970s.
During the 1960s, Yugoslavia’s Airforce possessed turbojet-powered aircraft of American origin, namely the Lockheed T-33, for schooling, training, and reconnaissance purposes, as well as the F-84G Thunderjet as a fighter bomber. Despite their excellent and long-serving performance in the JRV, these aircraft were phased out and handed over to Yugoslavia. In the latter part of the decade, they were replaced by the F-86E Sabre and F-86D Sabre. While the G-2 Galeb and Sabres covered two-thirds of their mission requirements, there was a need for a suitable aircraft to fulfill the remaining fighter-bomber missions.
Leveraging the successful development of the G-2 Galeb, the single-seat J-21 Jastreb was created using acquired and owned technology. It featured a more powerful engine, substantial armament, and advanced equipment designed for fighter-bomber tasks.
Design
The airframe of the G-2 Galeb was fully utilized for the development of the J-21 Jastreb. The front and cabin sections of the fuselage were modified to accommodate weapon installations and remove one seat from the pilot’s cabin. In the central part of the fuselage, slight modifications were made to accommodate a slightly more powerful Rolls-Royce Viper 20Mk 531 engine, providing a thrust of 13.3 kN. The front section of the hull houses three Colt Browning machine guns, each loaded with 130 rounds of ammunition (12.7 mm caliber). For the pilot’s safety, the cabin has an ejectable seat known as the “1B Foland.”
Operational history
The Soko J-21 Jastreb actively participated in combat operations as part of the Army and Air Defense Forces of the JNA (Yugoslav People’s Army) at the onset of the conflict in the Socialist Federal Republic of Yugoslavia in 1991. Subsequently, it served in the Army and Air Defense Forces of the Republika Srpska Army. However, the largest number of Jastrebs were decommissioned in 1996 by the Armed Forces of the Federal Republic of Yugoslavia based on the Subregional Agreement on Arms Control. In the early 21st century, a few Jastrebs remained operational by the air forces of Republika Srpska and Libya.
In the former Socialist Federal Republic of Yugoslavia (SFRY), the J-21 Jastreb primarily fulfilled tasks related to training and occupation of JRV (Yugoslav Air Force) units. It also had a significant role in reconnaissance operations. Following SFRY’s dissolution and the aircraft’s transfer to the RV RS (Republika Srpska Army) and RV FRY (Federal Republic of Yugoslavia), its combat capabilities became more prominent. The RV RS frequently employed the J-21 for air-to-ground missions.
On February 28, 1994, during a combat mission, six Jastreb aircraft of the Republika Srpska were attacked by two NATO F-16 aircraft in what is known as the Banja Luka incident. Four of the six J-21 Jastrebs were shot down, while the remaining two escaped. After signing the Dayton Agreement in 1995 and the cessation of hostilities, the Federal Republic of Yugoslavia retired all sixty-six Jastreb aircraft from service, while the Republika Srpska continued to utilize 11 aircraft.
Variants
The J-21 Jastreb had a prototype version, with only one copy produced. Similarly, the NJ-21 Jastreb, a two-seater training variant, also had a prototype with a single copy manufactured. The single-seat fighter-bomber J-21 Jastreb saw production of 119 units. Additionally, the two-seater training variant NJ-21 Jastreb was produced with 18 examples. The IJ-21 Jastreb was developed for reconnaissance purposes, with 38 units produced. An export variant known as the J-1E Jastreb was also manufactured, with 47 examples produced specifically for export purposes.
Technical specifications
| Country of origin: | Yugoslavia |
| Manufacturer: | SOKO Mostar, Yugoslavia |
| Designer: | Aeronautical Technical Institute (ATI) |
| Type: | light attack aircraft |
| Crew: | 1 |
| Introduced in service: | 1968 (first flight July 19, 1965) |
| Powerplant: | 1 × BMB (Rolls-Royce/Bristol Siddeley) Viper Mk 531 turbojet engine, 13.32 kN (2,990 lbf) thrust 2 × JATO units solid-fuelled rockets, 4.45 kN (1,000 lbf) thrust each |
| Fuel capacity: | 440 kg (970 lb) internal fuel + 435 kg (959 lb) in 2x 275 L (60 imp gal; 73 US gal) jettisonable wing-tip fuel tanks |
| Dimensions: | span 11.68 m / 38 ft 3.8 in length 10.88 m / 35 ft 8.3 in height 3.64 m / 11 ft 11.3in |
| Weight (empty): | 2,820 kg / 6,217 lb |
| Max. flight mass: | maximum take-off 5,100 kg / 11,244 lb |
| Maximum speed: | 443 kt / 510 mph / 820.76 km/h |
| Range: | 1520 km / 944 miles |
| Armament: | three 12.7-mm (0.5-in) machine guns with 135 rounds per gun; provision for 500 kg (1,102 lb) of disposable stores, including bombs, bomblet containers, flares, rocket-launcher pods, and gun pods carried on two inboard hardpoints, and for six 127-mm (5-in) air-to-surface rockets on outboard attachments |
| Operators: | Bosnia and Herzegovina, Serbia, Zambia |