The Republic of China, or Taiwan, is about to buy the long-range naval reconnaissance version of the General Atomics MQ-9 Reaper for high-altitude surveillance.

Taiwan is in negotiations to buy four MQ-9B SeaGuardian unmanned aerial vehicles from General Atomics Aeronautical Systems, Inc.

The price has been estimated at a minimum of $600 million for four drones, ground stations, spares, training and support. Taiwan will get an option to buy more SeaGuardians.

People close to the deal said the sale had been tacitly authorized by the U.S. Department of State. It is unclear, however, if the State Department has authorized sales of the air-to-surface missiles that normally arm the unmanned combat air vehicles.

Taiwan's purchase, however, must be approved by Congress. It will get formal notification of the sale in September. Congress has the power to block the deal but this seems unlikely given the existing anti-China sentiment in both Houses of Congress.

Taiwan asked to buy armed, U.S.-made drones early this year. Last week, the U.S. sent Taiwan pricing and availability data. Military analysts said this denoted official approval to proceed.

The remotely piloted SeaGuardian has a range of more than 11,000 kilometres (6,000 nautical miles), endurance of more than 40 hours and a speed of some 390 kilometres an hour. It has a ceiling of 12,000 meters (40,000 feet). Australia has ordered SeaGuardians, too.

The UAV can carry different payloads. The SeaGuardian's weaponized version can carry precision guided munitions such as AGM-114 Hellfire air-to-ground missiles and 500 pound (230 kilogram) GBU-12 Paveway II laser-guided bombs.

The U.S. government wants to sell as many weapons as it can to Taiwan because it says it faces the threat of a seaborne invasion by China. In 2019, it approved a potential sale to Taiwan of 108 M1A2 Abrams heavy tanks for around $2 billion. It sold antitank missiles and anti-aircraft munitions to Taiwan.

The largest arms request Taiwan has made is for 66 General Dynamics F-16V Fighting Falcon supersonic, air-superiority fighters to increase its self-defense capabilities. These will cost more than $13 billion.