India’s “Storm Spirit”

In 1956, the Indian government began to pursue a policy of “non-alignment” with both the West and the Communist Block. The pursuit of self-reliance in military aviation was part of that policy, and to that end, the government decided to replace the Indian Air Force British Hawker Hunter fighter-bombers with an indigenous design.

The Hunter Replacement Requirement was very ambitious. It called for a multi-role aircraft suitable for both high-altitude interception and low-level ground attack with a top speed of Mach 2.0 at its service ceiling of 60,000 feet and a combat radius of 500 miles.

The Indian government had little appreciation or interest in the technological hurdles. At the time India’s main aviation company, Hindustan Aircraft Limited possessed three design engineers, a design department of only 54, and a production engineering department of just 13.

There was no hangar space for the construction of prototypes, no machine shop for prototype engineering, no test equipment, structural test rigs or flight test laboratory.

HALs only design experience was with a basic propeller driven trainer and had only produced British Vampire fighters under license. There was not even a suitable runway from which the new aircraft could begin flight testing. The entire infrastructure had to be built from scratch.

India invited the famed German designer Kurt Tank, fresh from failure in a similar program in Argentina and currently teaching in India, to design the aircraft. Work on designing the new fighter, designated the HF-24 Marut (“Storm Spirit”) commenced in June 1957. Unusually, the mock up was a glider that was used for initial flight tests.

Tank quickly built a full team for HAL, and by 1961 the company had 18 German design engineers, a design department of 150, and a production engineering department with more than 100 personnel.

The Marut was a fine looking aircraft, very sleek, with an area-ruled fuselage and relatively small swept wings and tail surfaces. The wings had hydraulically-actuated ailerons and trailing-edge flaps which reverted to manual control with hydraulic failure, and a manually operated rudder. The pilot sat in a bubble canopy with a Martin-Baker zero-altitude ejection seat.

The armament was powerful — four 30 millimeter Aden cannon with 130 rounds per gun and an internal MATRA rocket launcher with 50 68-mm unguided rockets. The aircraft had four underwing hard points for bombs, rockets or drop tanks.
The HF-24 was designed  to use two afterburning British Orpheus BOr 12 engines with 8,170 pounds of thrust each, but the British dropped the BOr 12 program and the Indian government refused to pay for its continued development. It was a decision that was to permanently haunt the Marut program.

For the prototypes, the design team was forced to use non-afterburning 4,850 pounds Orpheus 703s installed side-by-side in the rear fuselage with highly visible, non-adjustable shock cones on the side mounted air intakes.

Assembly of the first HF-24 prototype began in April 1960. It flew for the first time on June 17, 1961, and made its first official flight a week later for the Indian Defence Minister. Meanwhile, the Indian government initiated a lengthy and ultimately unsuccessful search for an alternative power plant. In late 1961 they imported six Soviet Tumansky RD-9F engines used in the MiG-19 fighter, but they were rejected in 1963 because they were prone to surging and its overhaul life was unacceptably short.

The Egyptian E-300 turbojet was considered, but it failed to live up to expectations and was dropped. Bristol Siddeley proposed a new engine in 1964 but again the Indian government refused to underwrite development costs.

But rather than admit failure and shelve the grossly underpowered Marut, in late 1962 the Indian Government ordered 80 powered by the Orpheus engines, over Indian Air Force objections.

The IAF decided that, because of its low power, the Marut could only be used in the low level attack role, and this meant it had to be significantly modified.
The test aircraft underwent protracted service and weapon systems tests before they were ready for service. In the end, it took about 1,800 test flights before the first series production aircraft began to equip the Flying Daggers of the IAF’s 10 Squadron in 1967.

During the early years Maruts suffered from major serviceability problems because of the non-availability of spares, and the aircraft had other teething troubles that were not solved until 1970.

Notably, the gun vibrations were so excessive that the guns had to be harmonized after every two gun-firing sorties and, much more seriously, firing the guns also occasionally caused the canopy to blow off. Fortunately, this problem was fixed before the Maruts found themselves at war.

When the 1971 Indian-Pakistan War began, despite its limited power the Marut proved to be a fine combat aircraft. Its four 30 millimeter cannon gave it a formidable punch and its pleasant handling characteristics and ruggedness made it well liked by its pilots.

The twin engines and the well designed controls that reverted to manual whenever the hydraulic systems were shot out made it very survivable, and on at least three occasions Maruts recovered after one engine had been lost to ground fire.
More than 130 Maruts were sent to the IAF and they eventually equipped three IAF Squadrons until the early 1980s, when Jaguars and MiG-23BN/27s began to replace the Maruts.

In retrospect, while its lack of power made the Marut a mediocre performer, the program helped lay the infrastructure for the Indian aviation industry. When production ceased the Marut had around 80 percent indigenous content, HAL was manufacturing all the components and, most importantly, HAL had a full design and production team in place.

(For questions or comments, contact Dr. Michel at  marshall.michel@spangdahlem.af.mil.)