Operated by Air France on route proving flights the 521 was militarised in 1939 and operated by the Vichy government until stored at Marignane, finally being destroyed when axis troops retreated from advancing Allies.
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After the armistice in June 1940 it flew to Berre, near Marseilles, where it was finally wrecked by the retreating Germans in August 1944.
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The inaugural flight took place on 10 January 1935, followed by a demonstration flight in December 1935 via Dakar, North Africa to Natal, Brazil, then north to the French West Indies.
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On 30 December 1937 it set an FAI record carrying a payload of 18040 kg (39,770 lbs) to 2000 meters (6,562 ft) altitude at Biscarrosse, France.
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On the outbreak of World War II the Laté 521 was attached to the French Navy E.6 flotilla, based in Port-Lyautey, Morocco, and was used to patrol the North Atlantic.