HAL HF-24 Marut

During the 1950s, Hindustan Aircraft Limited (HAL) had developed and produced several types of trainer aircraft, such as the HAL HT-2. However, elements within the firm were eager to expand into the then-new realm of supersonic fighter aircraft.[2] Around the same time, the Indian government was in the process of formulating a new Air Staff Requirement for a Mach 2-capable combat aircraft to equip the Indian Air Force (IAF).[3] However, as HAL lacked the necessary experience in both developing and manufacturing frontline combat fighters, it was clear that external guidance would be invaluable; this assistance was embodied by Kurt Tank.

In 1956, HAL formally began design work on the supersonic fighter project.[4][2] The Indian government, led by Jawaharlal Nehru, authorised the development of the aircraft, stating that it would aid in the development of a modern aircraft industry in India.[5] The first phase of the project sought to develop an airframe suitable for travelling at supersonic speeds, and able to effectively perform combat missions as a fighter aircraft, while the second phase sought to domestically design and produce an engine capable of propelling the aircraft.[4] Early on, there was an explicit adherence to satisfying the IAF's requirements for a capable fighter bomber; attributes such as a twin-engine configuration and a speed of Mach 1.4 to 1.5 were quickly emphasised.[4]

During development, HAL designed and constructed a full-scale two-seat wooden glider to act as a flying demonstrator. Designated HAL X-241, this replicated production aircraft in terms of dimensions, control configuration, and aerofoil sections. The wheel brakes, air brakes, flaps, and retractable undercarriage were all actuated using compressed gas, with sufficient gas storage aboard for multiple actuations per flight.[6] On 3 April 1959, the X-241 flew for the first time, having been launched by aero-tow behind a Douglas Dakota Mk.IV BJ 449. A total of 86 flights were conducted prior to the X-241 receiving considerable damage as the result of a landing accident, after the nose undercarriage failed to extend.[6][7]

On 24 June 1961, the first prototype Marut conducted its maiden flight.[3][7] It was powered by the same Bristol Siddeley Orpheus 703 turbojets that had powered the Folland Gnat, also being manufactured by HAL at that time. On 1 April 1967, the first production Marut was delivered to the IAF.[7] While originally intended only as an interim measure during testing, HAL decided to power production Maruts with a pair of unreheated Orpheus 703s, meaning the aircraft could not attain supersonic speed.[3] Although originally conceived to operate around Mach 2, the Marut in fact was barely capable of reaching Mach 1 due to the lack of suitably powerful engines.[3][8]

The IAF were reluctant to procure a fighter aircraft only marginally superior to its existing fleet of British-built Hawker Hunters; however, in 1961, the Indian Government decided to procure 16 pre-production and 60 production Maruts.[7] Only 147 aircraft, including 18 two-seat trainers, were completed out of a planned 214.[3] After the Indian Government conducted its first nuclear tests at Pokhran, international pressure prevented the import of better engines, or at times, even spares for the Orpheus engines; this situation was one of the main reasons for the aircraft's early demise. The Marut never realised its full potential due to insufficient power. The Marut "was technically obsolete by the time it was first delivered in 1964".[3] Other authors have also commented on the Marut's relative obsolescence by the time it reached production.[9]

The Marut was described as "essentially a very long-drawn-out failure", and the aircraft's shortcomings were considered to be due to multiple factors.[10] Among these were the difficulties experienced in securing a suitable engine, which was principally a political issue; while arrangements were successfully established with the United Kingdom and Bristol Siddeley for HAL to domestically produce the Orpheus, it was only suitable as an interim measure as it lacked the power to enable the Marut to achieve supersonic speed.[11] The Indian Government refused a proposal made by Rolls-Royce to finance further development of the Orpheus, which had been specifically aimed at producing a more suitable engine for the Marut.[11][3]

Other envisioned alternative engines that might have been sourced from the Soviet Union, Egypt, or various European nations did not result in anything of substance.[3][12] The Gas Turbine Research Establishment also pursued their own development program to improve the Orpheus without external aid, which proceeded to the testing phase with some favourable results, but proved incompatible with the Marut.[13] As the particularities of a given airframe are typically heavily dependent on the engine used, the inability to improve the Marut's powerplant damaged its performance.[12] Despite experimentation with various engines, the Marut was never able to achieve supersonic speeds, which was viewed as a major failure.[4] IAF had anticipated the Marut being fitted with a considerably superior engine.[13][14]

The project was negatively affected by a lack of direction and management from the Indian Ministry of Defence.[12] A lack of coordination between the military, politicians, and industry is alleged to have been typical throughout the entirety of the programme, leaving many issues down to industry alone without guidance. Specifically, the government never sanctioned the development of an engine design team, nor were there assessments of HAL's capability to reverse engineer or to apply technologies from other projects, such as the work performed for the Folland Gnat.[15] HAL is claimed to have struggled to convince both the IAF and MoD that the design of the Marut was acceptable; much attention was given to the unacceptably high level of trail drag the airframe produced, as well as dissatisfaction with the Marut's speed and manoeuvrability, both of which were below IAF specification upon the aircraft's introduction.[12]

Tank had a major influence on the project, and accordingly of its shortcomings. While working on the Marut, he was criticized for a rigid stance on aspects of the design,[16] and he typically had little interest in lobbying the Indian government for funding to refine the design. In addition, however, elements of the IAF have been alleged to have held dismissive attitudes toward Tank and of his abilities, rarely coordinated with him on issues with the aircraft, which in turn exacerbated the type's performance issues.[15] The level of technological transfer between Germany and India on the project was subject to criticism as well.[17]

Limitations within the Indian aerospace industry, which lacked the infrastructure and scientific base to successfully produce an effective indigenous combat aircraft at that time,[5] forced a heavy reliance on foreign technologies and imported components.[2] HAL's willingness to undertake overly-ambitious defence projects may also be partially responsible for the project's outcome.[2] The Marut was not only heavily dependent on foreign-sourced materials, but was more expensive to manufacture the type in India than to have imported completed aircraft.[3] The level of indigenous components increased over time, reportedly reaching 70 per cent by December 1973.[7] The allocation of scarce resources to reproducing components that could have been readily imported represented a high level of opportunity cost to India.[5]

The IAF reportedly showed little confidence or interest in indigenous fighter technology, having openly expressed its preference for the French-built Dassault Ouragan as an alternative.[15] By the time the Marut entered mass production, the IAF had already purchased foreign-built fighters such as the Hawker Hunter and Sukhoi Su-7.[13] Following on from the Marut, HAL proceeded to produce larger quantities of both European and Soviet combat aircraft under license, such as the SEPECAT Jaguar, Mikoyan-Gurevich MiG-21, and Mikoyan MiG-27.[18]