4 (Base Aérea N.º 4, BA4) (IATA: TER, ICAO: LPLA), is a multi-use airfield near Lajes and 15 km (9.3 mi) northeast of Angra do Heroísmo[1] on Terceira Island in the Azores, Portugal.

In 1934, the Achada airfield was condemned due to its inadequate dimensions and adverse weather conditions, resulting in the construction of a landing strip of packed earth and a small group of support facilities by the Portuguese military at Lajes.

The military activities in the Azores grew in 1942, as the Gladiators began to be used to support allied convoys, in reconnaissance missions and on meteorological flights.

Using Lajes Field, the flying time relative to the usual transatlantic route between Brazil and West Africa was nearly cut in half from 70 to 40 hours.

[5] In 1945, two ZP-14 replacement blimps were sent from Weeksville, North Carolina, to the Bermudas and Lajes before going on to Craw Field (Kenitra Air Base) at Port Lyautey.

In 1947, the Portuguese Esquadra 41 started to operate from Lajes, equipped with Boeing SB-17, Grumman HU-16 Albatross, Douglas C-54 Skymaster and, later Sikorsky H-19 helicopters.

However, use of Lajes Field by the U.S. Department of Defense takes place under a U.S.-Portuguese Status of Forces Agreement (SOFA), separate and in addition to NATO arrangements.

The Cold War military importance of Lajes Field outweighed considerations about the Salazar Government's dictatorial rule over Portugal.

With the collapse of the Soviet Union and the Warsaw Pact, and end of the Cold War, P-3 operations at Lajes declined, and the Naval Air Facility was inactivated in the late 1990s.

Along with the aircraft came the U.S. European Command battle staff and flight crews from United States Air Forces in Europe.

[9] The Puma helicopters were replaced by the modern AgustaWestland AW101 Merlin: the Portuguese government purchased twelve units for SAR, CSAR and Fisheries enforcement.

In order not to compromise the SAR mission, the Portuguese Air Force decided to reactivate the Puma fleet: in July 2008 a formation of four Puma helicopters made the trans-Atlantic crossing from Beja to Lajes via Porto Santo Airport on Porto Santo Island and Santa Maria Airport on Santa Maria Island.

Beginning in 1997, large scale fighter aircraft movements under the new USAF operating concept known as the Air Expeditionary Force (AEF) filled the Lajes flightline.

Lajes Field services aircraft from various nations, including Belgium, Brazil, Canada, Colombia, Denmark, France, Germany, Greece, India, Israel, Italy, the Netherlands, Pakistan, Poland, Qatar, Russia, Spain, Sweden, the United Kingdom, and Venezuela.

The next decade expects to see a rise in the number of U.S. Department of Defense aircraft to transit Lajes supporting the newly created AFRICOM.

In August 2006, Portuguese news agencies reported that both governments were in discussions for a new agreement that could allow the use of Lajes for the training of a permanent F-22 Raptor squadron.

Portugal has explored contingencies in the event the United States military eventually abandons Lajes, including the possibility of entering an agreement with the People's Republic of China.

On June 27, 2012, an airplane carrying Premier Wen Jiabao made a four-hour stop at Lajes during which time he toured the island.

[12] The base supports NATO and non-NATO armed forces assets crossing the Atlantic for transport, VIP, exercise, relief or humanitarian duties.

In the past five years, large Antonov An-124 and An-225 aircraft have been seen frequently transporting outsized cargo for destinations in North and South America.

In addition, a small commercial aviation terminal handles scheduled and chartered flights from North America and Europe, especially mainland Portugal.

The group provides base and en route support for the U.S. Department of Defense, NATO, and other authorized aircraft transiting the installation.

Due to the global economic crisis, the US government decided to reduce the military contingent at Lajes to no more than 170 active duty personnel.