Pakistan will buy four frigates from China, its longtime ally and main supplier of military equipment, the Defense Ministry said Monday. Senior defense officials from Pakistan and China signed the deal for the warships, long-sought by Pakistan, in Rawalpindi, a city near the capital Islamabad, the ministry said in a statement. "These F-22P frigates will be equipped with organic helicopters specially designed for anti-submarine warfare, surface-to-surface and surface-to-air missiles along with numerous associated self-defense systems," the statement said. It said China will sell the boats on the basis of "transfer of technology." A navy official said on condition of anonymity that the term means that some of the ships will be made in Pakistan.