How does the Arjun compare against tanks of the other great powers?
Tanks
Russian T-90--47-ton, small, 3-man tanks with autoloaders. Below-average armor protection. 20-26 hp/ton; superb reliability and unrefueled combat range (700km). Low ground pressure; armament is average at best and not really equipped to fight a tank duel on a one-on-one basis against other modern tanks. Cheap ($2.5-$4.5M per).
Russia uses its tanks to take ground. It makes 3-man tanks because it needs a lot of tanks for a shrinking manpower base. It has average engines in terms of horsepower, because a) their tanks are comparatively light and b) squeezing out another 10km/h on a tank that can already go 50-60km/h is not really worth it in terms of how much ground it can cover. Reliability and unrefueled range are a must because in their doctrine armor will be fighting operational exploitation battles far away from from friendly repair and resupply. One-on-one duelling is not important because their doctrine calls for groups of enemy armor to be either "swarmed and surprised" with superior numbers of faster tanks or ignored altogether, exploiting again, their tank's superior mobility.
What is it suited for? Fighting chaotic cavalry-style battles on the wide-open plains of Eastern Europe, Siberia, or Mongolia, either before, during, or after a nuclear holocaust.
US M1A2--61-ton, large, 4-man tanks. Superb armor protection, including against urban warfare threats such as RPGs fired from rooftops. 24 hp/ton; average reliability (gas turbines are difficult to maintain); below-average operating range (426km). Somewhat higher ground pressure. Superb fire control, reload speed, and main gun to engage large numbers of enemy tanks at once. Extremely expensive ($8M per).
The US uses its tanks to punch holes. The US is a purely offensive and expeditionary force; the Abrams is essentially the tip of the US offensive spear. It doesn't need to worry about refuelling because usually it operates in the context of brigades and regiments already bathed in the best logistics network possible. However, since it expects to perform infantry support in the context of spearhead operations, it needs a thick hide and the ability to pump out a lot of accurate tank fire at once.
What is it suited for? Breaching (or killing) an opponent pinned down by the US Air Force into static defensive lines.
German Leopard 2A7--62-ton, large, 4-man tanks. Superb armor protection, but not necessarily against urban warfare threats--even thicker armor than the M1A2 in front glacis and turret. 24hp/ton; superb reliability; average operating range (550km). Somewhat higher ground pressure. Superb fire control, reload speed, and main gun--same as M1A2. Slightly expensive ($5.5M per).
Germany uses its tanks to defend against and hunt down other tanks. The Leopard is a superb tank-on-tank duellist and a long-range killing machine versus enemy armor. It is reliable, reasonably mobile, and has good range. The downside? A Leopard is a "tanker's tank", which means it should avoid being drawn into city fights. Also, it, like the Abrams, is heavy, which means in a situation where a lot of larger bridges have been knocked out, the Leopard suffers severe limitations on tactical mobility.
What is it suited for? Killing Russian tanks.
Chinese Type 99--57-ton, average-sized, 3-man tanks. Above-average armor protection. 28 hp/ton with 80km/h top speed; superb reliability; above-average operating range (600km) -- uses essentially the same engine as the Leopard 2A7. Average ground pressure. Superb fire control but not necessarily good reload speed. Decent main gun. Cheap ($2M per).
China uses its tanks to hunt non-tank targets and ambush enemy armor. For example, China would use its tanks to kill enemy "soft" divisions, like US Stryker brigades, for instance. The Type 99 has the speed to chase down wheeled and tracked IFVs, and great accuracy and firing range but not the sustained fire rate necessary for tank duelling. The high hp/weight ratio also lets the Type 99 climb steeper slopes than other tanks can, dramatically improving its capabilities in mountain combat.
What is it suited for? Counterattacking and ambushing American formations in mountainous North Korea, or hunting down insurgents in Central Asia.
Indian Arjun Mk II--58 ton, average-sized, 4-man tanks. Above-average armor protection. 24 hp/ton with 72km/h top speed; average reliability; below-average operating range (450km). Heavy ground pressure. Superb fire control and reload speed. Above-average main gun. Relatively cheap ($3M per).
India uses Arjuns as cheaper versions of the Abrams--to punch holes. India's tanks are not designed to operate in extended tank duels or cover ground; they are built to rapidly dismantle fixed defensive lines and open gaps for other units to cross. Indian tanks are given limited operating range not because the Indian Army has great logistics but because Pakistan is a small country. Also, they are heavy, but since their main job is crossing a desert between India and Pakistan, collapsing a bridge or two is not really a problem.
What is it suited for? Invading Pakistan in a short, swift campaign. It outguns all Pakistani armor, but lacks the range to invade any country larger than Pakistan without lots of refuelling capacity; capacity which the Indian Army currently lacks.
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This, incidentally, is why, even though modern tank technologies have converged in the major powers to some degree, all major powers have radically different tank designs. This is also why direct tank on tank comparisons are relatively useless, as all modern tanks are designed with somewhat different battles in mind.
With this in mind, the Arjun is a wonderful tank for the central purpose of the Indian Army--repelling or mounting offensive operations against Pakistan. Its thick armor and excellent fire control do the job. But in other roles, however, its high ground pressure and fuel-inefficiency will work against it. India would be wise to retain one or two regiments of T-90s or lighter tanks to give the Army some degree of additional flexibility.