During World War II, the designation of the airfield was changed to Air Base No.4 and the Portuguese government expanded the runway, sending troops and equipment to Terceira, including Gloster Gladiator fighters.
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.
In addition, the first Portuguese Junkers Ju 52 arrived in July 1942 to fly cargo missions.

By 1943, the British and American armed forces were allowed basing rights in Portugal.
Within a month of disembarking on Terceira in October 1943, the Royal Air Force had laid pierced steel planking to lengthen the runway at Lajes Field, allowing the Royal Air Force to begin patrols.
The first attack on a German U-boat was conducted in November, sinking the submarine; this attack was followed by a dozen more attacks on U-boats by the end of February 1944, after which German forces stayed clear of the British and American patrol areas.
The Azores enabled British and American airmen to protect Allied shipping in the area.

On 1 December 1943, British and U.S. military representatives at RAF Lajes Field signed a joint agreement outlining the roles and responsibilities for the United States Army Air Forces (USAAF) and United States Navy (USN) at Lajes Field.
The agreement established guidelines and limitations for the ferrying of aircraft and the transport aircraft to Europe via Lajes Field.
In return, the US agreed to assist the British in improving and extending existing facilities at Lajes.
Air Transport Command transport planes began landing at Lajes Field immediately after the agreement was signed.
By the end of June 1944, more than 1,900 American airplanes had passed through this Azorean base.
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.

Lajes Field was one of the two stopover and refueling bases for the first transatlantic crossing of non-rigid airships (blimps) in 1944.
The USN sent six Goodyear-built K-ships from Naval Air Station South Weymouth in Massachusetts to their first stopover base at Naval Station Argentia, Newfoundland and then on to Lajes Field in the Azores before flying to their final destination at Port Lyautey (Kenitra), French Morocco.
From their base with Fleet Air Wing 15 at Port Lyautey, the blimps of USN Blimp Squadron 14 (ZP-14 or Blimpron 14) conducted night-time anti-submarine warfare (ASW) to search for German U-boats around the Strait of Gibraltar using magnetic anomaly detection (MAD).
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.
During World War II, the designation of the airfield was changed to Air Base No.4 and the Portuguese government expanded the runway, sending troops and equipment to Terceira, including Gloster Gladiator fighters. 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. In addition, the first Portuguese Junkers Ju 52 arrived in July 1942 to fly cargo missions.
By 1943, the British and American armed forces were allowed basing rights in Portugal. Within a month of disembarking on Terceira in October 1943, the Royal Air Force had laid pierced steel planking to lengthen the runway at Lajes Field, allowing the Royal Air Force to begin patrols. The first attack on a German U-boat was conducted in November, sinking the submarine; this attack was followed by a dozen more attacks on U-boats by the end of February 1944, after which German forces stayed clear of the British and American patrol areas. The Azores enabled British and American airmen to protect Allied shipping in the area.
On 1 December 1943, British and U.S. military representatives at RAF Lajes Field signed a joint agreement outlining the roles and responsibilities for the United States Army Air Forces (USAAF) and United States Navy (USN) at Lajes Field. The agreement established guidelines and limitations for the ferrying of aircraft and the transport aircraft to Europe via Lajes Field. In return, the US agreed to assist the British in improving and extending existing facilities at Lajes. Air Transport Command transport planes began landing at Lajes Field immediately after the agreement was signed. By the end of June 1944, more than 1,900 American airplanes had passed through this Azorean base. 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.
Lajes Field was one of the two stopover and refueling bases for the first transatlantic crossing of non-rigid airships (blimps) in 1944. The USN sent six Goodyear-built K-ships from Naval Air Station South Weymouth in Massachusetts to their first stopover base at Naval Station Argentia, Newfoundland and then on to Lajes Field in the Azores before flying to their final destination at Port Lyautey (Kenitra), French Morocco. From their base with Fleet Air Wing 15 at Port Lyautey, the blimps of USN Blimp Squadron 14 (ZP-14 or Blimpron 14) conducted night-time anti-submarine warfare (ASW) to search for German U-boats around the Strait of Gibraltar using magnetic anomaly detection (MAD). 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.
Lajes Field