The MBT Arjun Mk I (Hindi: एम बी टी अर्जुन मार्क I) is an indigenously developed Indian main battle tank in service with the Indian Army. The tank is named for Arjuna (Hindi: अर्जुन), the archer prince who is the protagonist of the Indian epic Mahābhārata (Sanskrit: महाभारतम्). The development of the Arjun was slow and arduous. Beginning in the wake of the 1971 Bangladesh Liberation War, India issued a requirement for a new main battle tank to replace the Vijayantā (Hindi: विजयंता) and supplement the T-72. The project was funded in 1974, and development fully began in 1976 when the Combat Vehicles Research and Development Establishment (CVRDE) was created to oversee the programme. India collaborated with Krauss-Maffei Wegmann, the developers of the Leopard 2, to develop the vehicle. Prototypes were constructed between 1984 and 1987, well behind schedule, and finally handed over in 1989 for testing – testing which only began in 1993 and continued until 1996. Production was only finally approved in 2000 with an order for 124 vehicles, and the Arjun entered service in 2004, over 30 years after the project began. All 124 vehicles were delivered by 2011. Of the originally planned 2,000 vehicles, the 124 serial-production vehicles, along with 15 pre-production vehicles and two Arjun Mk IA prototypes, remain the only vehicles to have been produced, though 118 Mk IA vehicles are on order.

The Arjun Mk 1 was introduced in Update 2.59 "Sky Odyssey". It is, in effect, a Leopard 2A4 that trades turret blowout panels for better ammunition and a better thermal sight. The 120 mm gun with its MK-II FSAPDS round is very strong and capable of penetrating most vehicles at the tier. The vehicle has capable turret armour and is quite mobile, with a maximum speed of 70 km/h. Generally, the Arjun is a very well-balanced vehicle, though, like nearly every other MBT, it does suffer from rather poor hull armour, and the lack of blowout panels means that hits to the turret ammunition rack are usually fatal.