The defects had been pointed out in the tank's power plant and suspension system, Defence Minister AK Antony said in a written reply in the Lok Sabha recently.

The air filter of the tank's German-built MTU 838 Ka-501 engine had been found to be defective during trials and help had been sought from the manufacturers to rectify this.

"The cause of (the) defect was analysed and rectified in consultation with the specialists of MTU," the minister stated.

The piston rods of the tank's hydro pneumatic suspension unit had also failed during trials and this too had been rectified, Antony added.

The minister's reply was, however, silent on a dozen-odd other defects that the Indian Army is reported to have pointed out in the tank.

These include a deficient fire control system, inaccuracy of its guns, low speeds in tactical areas - principally deserts - and its inability to operate in temperatures over 50 degrees Celsius.

The army had, for the first time, deployed the Arjun in a five-day war game it conducted in the deserts of Rajasthan in April-May - and afterwards professed to be unsure of the role it would perform.

"We have to make sure the troops are not exposed to any disadvantage," Indian Army chief Gen JJ Singh replied cryptically when asked about Arjun's performance during the war game.

"We will draw lessons from the exercise on which area they (the Arjuns) can be best exploited.

After the exercise, the tanks had gone back to manufacturer Heavy Vehicles Factory at Avadi in Tamil Nadu for rectifying some defects.

These tanks have now been handed back to the army and are undergoing field trials that end in September. After that, the army will submit another report on their performance to the Defence Ministry.

At a review meeting in April with the tank's developer, Defence Research and Development Organisation (DRDO), Antony is known to have asked it to get its act together to rectify the defects or the government might have to take another look at the entire programme.

Parliament's Standing Committee on Defence has, in two reports earlier this year, remarked adversely on the slow pace of Arjun's development and asked the DRDO to quicken the process.

The Indian Army laid down its qualitative requirement (QR) for the Arjun in 1972. In 1982, the DRDO announced that the prototype was ready for field trials. However, the tank was publicly unveiled for the first time only in 1995.

Arjun was originally meant to be a 40-tonne tank with a 105 mm gun. It has now grown to a 50+tonne vehicle with a 120 mm gun.

The tank was meant to supplement and eventually replace the Soviet-era T-72 MBT that was first inducted in the early 1980s. However, delays in the Arjun project and Pakistan's decision to purchase the T-80 from Ukraine prompted India to order 310 T-90s, an upgraded version of the T-72, in 2001.

Of these, 186 were built at Avadi and an agreement was also signed for the licensed production of another 1,000 T-90s.

With the Arjun development delayed still further, India last year signed a fresh contract with Russia to buy 330 more T-90s.