By the late 1970s, Indian Army HQ had decided to acquire new-generation replacements for its UK-origin fleet of Royal Ordnance Factories-built Centurion and Vijayanta MBTs, which are based on the licensed production of the Vickers MBT, and consequently, paper evaluations concerning the firepower and mobility characteristics of the two principal contenders being offered for full in-country production—AMX-40 developed by GIAT Industries of France, and the Chieftain 800 (which later evolved into the Challenger 1 from Royal Ordnance Factories (then owned by British Aerospace PLC)—were conducted by the Indian Army.
Between these two contenders, the Army had by early 1980 zeroed in on the 43-tonne AMX-40 MBT, which was still on the drawing boards and was meant to be powered by a 1,100 hp Poyaud V12X 12-cylinder diesel engine coupled with a LSG-3000 automatic power shift transmission built by RENK Aktiengesellschaft of Germany (offering a power-to-weight ratio of 25.6 hp/tonne, and armed with a 120 mm smoothbore cannon.
However, AMX-40 had only marginal protection by the standards of 1980's.
After coming back to power, the Indian Prime Minister Indira Gandhi requested additional evaluation, including MBTs from the USSR, following which the Soviet Union's Ministry of Foreign Economic Relations (which after 1991 morphed into Oboronexport, then Rosoboronservice and ultimately Rosoboronexport State Corp) made a formal offer to India's Ministry of Defence (MoD) for supplying the 37-tonne T-72M Ob'yekt 172M-E4 MBT off-the-shelf, and according an approval for licensed-production of the 41.5-tonne T-72M-1982 Ob'yekt 172M-E6 to the MoD-owned Heavy Vehicles Factory (HVF) in Avadi.
By early 1981, two T-72Ms—powered by a 780 hp diesel engine, armed with 125 mm 2A46M smoothbore gun and offering a power-to-weight ratio of 20 hp/tonne, were subjected to an exhaustive series of in-country firepower and mobility trials by the Army.
After review of trial results, T-72M and T-72-1982 (powered by a Model V-84MS four-stroke 12-cylinder multi-fuel engine developing 840 hp and offering a power-to-weight ratio of 18.8 hp/tone) were selected as Army's future MBTs, and a procurement contract for 2,418 T-72s was subsequently inked.

Ajeya MK1 – Indian version of the T-72M1.
In parallel with buying various T-72M off-the-shelf from the Soviet Union, India also launched its domestic production at Heavy Vehicles Factory.

Ajeya MK2 – Indian version of the T-72M1 with ERA and banks of 6 smoke grenade-launchers on each side.

Combat Improved Ajeya For a rather long time the Indian Army did not intend to modernize its T-72 tanks since it was relying on their own tank project the Arjun.
However, the Arjun program had been undergoing difficulties.
As a result, they adopted the Operation Rhino plan aimed at re-equipping 1,500 T-72M1 tanks.
The upgrade program provides for installation of a Polish SKO-1T DRAWA-T fire control system/thermal imager supplied by the Polish PCO/Cenzin (from PT-91 Twardy), DRDO explosive reactive armour, a navigation system from Israel's Tamam, German Litef or South African RDI, a locally developed laser illumination warning system, new radios manufactured by Tadiran or GES Marconi and an improved NBC protection system will be fitted.
The tank is planned to be powered by a 1,000 hp (750 kW) S-1000 engine made by the Polish firm PZL-Wola (also from PT-91 Twardy).
It is also upgraded with new fire detection and suppression systems and laser warning systems on either side of the turret.
Indian sources often say that 1,800–2,000 T-72M1 tanks will be upgraded top to bottom while the rest will undergo only partial improvement.

Tank EX – Indian integration of the Arjun turret onto the T-72 hull, Prototype only.
Did not enter production as it was rejected by the Indian Army.
By the late 1970s, Indian Army HQ had decided to acquire new-generation replacements for its UK-origin fleet of Royal Ordnance Factories-built Centurion and Vijayanta MBTs, which are based on the licensed production of the Vickers MBT, and consequently, paper evaluations concerning the firepower and mobility characteristics of the two principal contenders being offered for full in-country production—AMX-40 developed by GIAT Industries of France, and the Chieftain 800 (which later evolved into the Challenger 1 from Royal Ordnance Factories (then owned by British Aerospace PLC)—were conducted by the Indian Army. Between these two contenders, the Army had by early 1980 zeroed in on the 43-tonne AMX-40 MBT, which was still on the drawing boards and was meant to be powered by a 1,100 hp Poyaud V12X 12-cylinder diesel engine coupled with a LSG-3000 automatic power shift transmission built by RENK Aktiengesellschaft of Germany (offering a power-to-weight ratio of 25.6 hp/tonne, and armed with a 120 mm smoothbore cannon. However, AMX-40 had only marginal protection by the standards of 1980's. After coming back to power, the Indian Prime Minister Indira Gandhi requested additional evaluation, including MBTs from the USSR, following which the Soviet Union's Ministry of Foreign Economic Relations (which after 1991 morphed into Oboronexport, then Rosoboronservice and ultimately Rosoboronexport State Corp) made a formal offer to India's Ministry of Defence (MoD) for supplying the 37-tonne T-72M Ob'yekt 172M-E4 MBT off-the-shelf, and according an approval for licensed-production of the 41.5-tonne T-72M-1982 Ob'yekt 172M-E6 to the MoD-owned Heavy Vehicles Factory (HVF) in Avadi. By early 1981, two T-72Ms—powered by a 780 hp diesel engine, armed with 125 mm 2A46M smoothbore gun and offering a power-to-weight ratio of 20 hp/tonne, were subjected to an exhaustive series of in-country firepower and mobility trials by the Army. After review of trial results, T-72M and T-72-1982 (powered by a Model V-84MS four-stroke 12-cylinder multi-fuel engine developing 840 hp and offering a power-to-weight ratio of 18.8 hp/tone) were selected as Army's future MBTs, and a procurement contract for 2,418 T-72s was subsequently inked.
Ajeya MK1 – Indian version of the T-72M1. In parallel with buying various T-72M off-the-shelf from the Soviet Union, India also launched its domestic production at Heavy Vehicles Factory.
Ajeya MK2 – Indian version of the T-72M1 with ERA and banks of 6 smoke grenade-launchers on each side.
Combat Improved Ajeya For a rather long time the Indian Army did not intend to modernize its T-72 tanks since it was relying on their own tank project the Arjun. However, the Arjun program had been undergoing difficulties. As a result, they adopted the Operation Rhino plan aimed at re-equipping 1,500 T-72M1 tanks. The upgrade program provides for installation of a Polish SKO-1T DRAWA-T fire control system/thermal imager supplied by the Polish PCO/Cenzin (from PT-91 Twardy), DRDO explosive reactive armour, a navigation system from Israel's Tamam, German Litef or South African RDI, a locally developed laser illumination warning system, new radios manufactured by Tadiran or GES Marconi and an improved NBC protection system will be fitted. The tank is planned to be powered by a 1,000 hp (750 kW) S-1000 engine made by the Polish firm PZL-Wola (also from PT-91 Twardy). It is also upgraded with new fire detection and suppression systems and laser warning systems on either side of the turret. Indian sources often say that 1,800–2,000 T-72M1 tanks will be upgraded top to bottom while the rest will undergo only partial improvement.
Tank EX – Indian integration of the Arjun turret onto the T-72 hull, Prototype only. Did not enter production as it was rejected by the Indian Army.
T-72 operators and variants