The Indian army will test an upgraded version of the indigenous Arjun main battle tank, the Mark II, within three months, defense research officials said.

"We have incorporated 56 of the total 89 improvements recommended in Arjun Mark II after the last test in Pokhran in Rajasthan," an official of the Defense Research and Development Organization said.

"We are hopeful of the next test, which is scheduled in December this year or January next year," the DRDO source said.

The Press Trust of India reported that the trials will include firing of the LAHAT missile, which has a range of 4-5 miles.

The Arjun's 120mm rifled main turret gun can fire the Israeli-made laser-homing anti-tank guided missile LAHAT, first in service in Israel in 1992. It was designed primarily for the Merkava tanks' 105mm and 120mm guns but it can be used by all 105mm and 120mm guns, including some low-recoil, low-weight guns fitted to armored cars.

The Indian army, which has 142 Mark II tanks on order, will put the vehicle through its final trials in June.

"Once Arjun Mark II comes out successfully through the integrated testing in June next year, the production of the latest version of Arjun tanks will start in Heavy Vehicles Factory," the DRDO source said.

The Arjun is made by Heavy Vehicles Factory in the specifically military manufacturing town of Avadi -- an acronym for Armored Vehicles and Ammunition Depot of India. Avadi is a coastal town of around 250,000 and about 15 miles from Chennai on the southeastern tip of India.

The Mark II is being developed by the Combat Vehicles Research and Development Establishment and will be in use from 2014.

Some of the major improvements include changes in the commander's panoramic sight to include a laser range finder and night vision capability. A stronger drive train and improved track is being developed to allow for larger weapons and thicker armor plating.

The announcement of final trials for the Mark II come after only months since the Mark I was officially inducted into the army but only after suffering nearly 40 years of delays. The tanks were inducted into the Indian army's 75th Armored Regiment in March.

At the same time, India began the retirement of its Russian T-55 tanks after 40 years of service.

The induction took place at the military base in Jaisalmer in the state of Rajasthan, around 360 miles west of the capital Jaipur, during the 39th anniversary of the creation of the 75th Armored Regiment.