Imperial Iranian Armored units were supplied with medium and light tanks of American and British origin, and about 1200 Brithish-maded Chieftain tanks were being delivered to augment the 780 in the inventory. Armored personnel carriers were from the United States and the Soviet Union and antitank missiles from the United States and France.

In 1971, Iran placed an order with Royal Ordnance (RO) of the UK for 707 modified Chieftain Mk 3 and Mk 5 MBTs, plus a quantity of armoured recovery vehicles (ARVs) and armoured vehicle-launched bridges (AVLBs) based on the Chieftain MBT chassis, all of which were delivered by early 1978. Most of these were built by RO Leeds, subsequently taken over by Vickers Defence Systems, which built all the ARVs. Iran also took delivery of 187 improved Chieftains called the FV4030/1 (a development of the Chieftain Mk 5 used by the British Army) for it's operational needs. In all, 187 of the FV4030/1, were supplied.
In 1974, Iran ordered 125 Shir Iran 1 (FV4030/2s) and 1,225 Shir Iran 2 (FV4030/3s) MBTs for delivery from 1980 - but the order was cancelled in 1979 after the fall of the Shah and before deliveries could begin from Royal Ordnance Leeds.
If the Shir 2 MBTs had been delivered, the Iranian Army would have had the best-protected MBT in the region because the hull and turret incorporated the advanced Chobham armour system for a high level of battlefield protection over the frontal arc. In 1979, Jordan bought 274 Shir 1 MBTs, designated the Khalid. After the Iranian Revolution the "Shir Iran 2" project was taken over by the British Army and the end result was Challenger later redesignated as Challenger 1 in service with the British Army since 1983.

Standard equipment includes thermal sights, gun stabilization NBC system as well as mounting points for external fuel tanks at the rear and Combat Dozer Blade at the front.