Previous tanks donated by North Atlantic Treaty Organization (NATO) members have been in the form of refurbished Russian tanks, mostly upgraded early-model T-72 tanks considered (at best) slightly inferior to the newest Russian tanks. Earlier donations such as Javelin anti-tank and Stinger anti-aircraft missiles are seen as more defensive weapons, while HIMARS guided rockets are more of an indirect support weapon.
Though detractors (including the Kremlin) scoff that Western tanks will be lacking in number and quality against the latest Russian tanks, such as the T-72B3 and T-90, it is actually widely accepted that the Leopards and Challengers are superior.
In particular, the standard Russian 125mm armour-piercing shells have been proven to be unable to penetrate the Challenger 2’s frontal armour (where it is the thickest) during the one occasion they have seen combat in the 1991 Persian Gulf War.
These Western tanks are significantly heavier on account of thicker armour and better protection. More importantly, they have better gunsights and optics, improving the likelihood of successfully hitting opponents with the first shot, an important consideration in tank-versus-tank combat.