Bayandor-class

The Bayandor-class vessels originated as patrol frigates constructed in the 1960s under a United States Mutual Assistance Program. Built with American funding, the ships were designed for immediate transfer upon completion to allied navies. The program resulted in four vessels for Iran, with two comparable half-sisters also constructed for the Royal Thai Navy. The Iranian ships entered service between 1964 and 1969.

Classified as corvettes, these ships have undergone significant modifications over their extensive service lives. As originally delivered, they were configured for anti-submarine warfare, equipped with depth charge racks and forward-mounted projectile launchers. This equipment was later removed, and their armament was progressively updated. Throughout the 1980s and 1990s, their anti-aircraft gun systems were replaced and upgraded. A comprehensive refit and overhaul program in the 2010s saw the installation of modern systems, including new radar and fire-control systems, anti-ship cruise missiles, a rapid-fire dual-purpose main gun, and new anti-aircraft cannons. The modernization also included overhauls of the propulsion, fuel, and heat converter systems.

Of the four corvettes originally delivered, only two remain in active service with the Islamic Republic of Iran Navy. Two vessels of the class were sunk in 1980 during the Iran-Iraq War, destroyed by Iraqi anti-ship missiles and aerial bombs. The two surviving ships have been subject to extensive refits to prolong their operational life, with one major overhaul reportedly taking twenty months to complete before the vessel returned to the fleet in 2013.