From 1939 until January 1944, the intelligence services of Germany and Italy, with the assistance of the Spanish government, maintained a network of stations in the vicinity of the Strait of Gibraltar.

The German Abwehr and the Italian Servizio Informazioni Militare (Military Intelligence Service [1925–1949]) established a network of ship-watching positions along the Strait of Gibraltar in Spain and Spanish Morocco during the early years of World War II.

The station at Algeciras, which was directly across the Bay of Gibraltar from the British territory, was the most important and radioed at least twenty reports each day to Abwehr headquarters in Berlin.

During their discussion on 27 May, Hoare presented a detailed account of German activities in Spain and indicated that petrol supplied by Allied countries had been used as part of the construction of the facilities.

[6] Franco denied that the network existed and claimed that the German personnel were providing technical assistance to Spanish coastal artillery batteries.

[6] While these sites were no longer operational by mid-July, the Allies learned from Ultra decrypts that the Germans were installing the equipment in new locations on Spanish territory.

Following this engagement, the British Chiefs of Staff Committee again considered countermeasures against the bolometer sites; the Governor of Gibraltar and Special Operations Executive proposed direct attacks on the facilities and the head of the Royal Navy advocated jamming them.

During a meeting held on 25 August, the Chiefs of Staff decided to make another diplomatic protest, which was formally lodged with the Spanish Government in October.

[10] The bolometer sites were dismantled during late 1942 and on 29 December that year, after the Spanish Government directed Canaris to cease intelligence activities in Spain to avoid giving the Allies a pretext to invade the country.

[1] In 1943, Jones found that a German Elektra Sonne station was being set up near Lugo in north-west Spain as part of a navigation system for aircraft and U-boats.