The Soviet-era T-55 is the most numerous tank in the Iraqi arsenal, and has been involved in several fierce tank battles during the current war.
Its poor showing against the modern US M1 Abrams and British Challenger 2 tanks in these actions have highlighted its deficiencies.
This is not surprising given the design of the T55, once the mainstay of Soviet armoured divisions, dates back to 1946.
The T55 and its predecessor are based on the T34, one of the most acclaimed tanks of World War II. The T54 first entered service in 1949, and successive updates led to the introduction of the T55 in 1958.
More of the T-54 and the T-55 have been made than any other tank.
As well as being made in Russia they were also produced in China, under the names Type 59 and Type 69. Thousands of T55s and derivatives have been exported to nearly 60 countries.
Some of them saw action with the Northern Alliance in Afghanistan.
Iraq is believed to have had more than 2,500 T55s of various models before the 1991 Gulf War, with more than 1500 thought to have been destroyed during the war, many in one-sided fights with coalition tanks.
Iraq's remaining T55s have been the subject of upgrades, with some thought to have had their 100mm guns replaced with more powerful and modern 105mm or 125mm guns.
It is also thought some have received extra armour, while others have had their engines and cooling system replaced to make them more effective in desert conditions.
But the T55's days as a front-line fighting tank ended years ago.
The T55 is much smaller than the M1 or the Challenger 2, with much thinner armour. Its rounded turret offers a low profile suitable for fighting when much of the tank is shielded by a slope or barricade.
Its gun cannot move up or down as much as more modern tanks and it is also unable to move and fire at the same time, another major handicap.
Its armour is too thin to withstand the uranium-depleted shells used by modern tanks, while the T55's own 100mm is too light to knock out the heavily armoured M1s or Challengers.
It is, however, still a danger to armoured personnel carriers such as the Bradley and the British Warrior.
T55 medium tank
100mm rifled main gun (original); some Iraqi examples have 105mm or 125mm guns
1 x 7.62mm machine gun, 1 x 12.7mm anti-aircraft machine gun