Shortly after the outbreak of the Second World War, the Laté 521 were taken over by the French Navy, who typically operated the type as a long distance maritime patrol aircraft.

During the early 1930s, French aircraft manufacturer Groupe Latécoère set about designing a new large flying boat, which was intended to perform long range flights, carrying both passengers and air mail.

The four inboard water cooled engines, which were mounted as tandem push-pull pairs and intended to be capable of generating up to 750 kW (1,000 hp), enabled the aircraft to attain a maximum design speed of 260 km/h (160 mph).

The stub-wings, hinged to the bottom of the hull, each carried a sponson to provide additional stability upon the water, as well as housing large fuel tanks and featuring an airfoil section to assist during takeoff runs.

[5] A large number of stiffeners were present throughout the stub-wings to achieve a relatively stress-resistant construction, conveying and distributing stresses across the frames and hull spars.

The structure of the wing was internally braced by a combination of duralumin tubular tie rods and round high-tensile steel tubing.

[7] On the lower level, there was a salon occupied by 20 armchairs and tables, along with six deluxe double cabins, each with its own bathroom, and seating for a further 22 passengers, a kitchen, a bar, a lavatory, and a baggage hold.

The more compact and narrower upper level of the hull featured seating for 18 passengers, along with a storage compartment, a second kitchen and bar, and another lavatory.

On 30 December 1937, the type established a new Fédération Aéronautique Internationale (FAI) record, carrying a payload of 18,040 kg (39,770 lb) at an altitude of 2,000 m (6,600 ft) while flying over Biscarrosse, France.

[citation needed] On the outbreak of the Second World War, the Laté 521 was pressed into service with the French Navy, all aircraft were attached to the flotilla E.6, based in Port-Lyautey, Morocco, where they performed maritime patrol flights over the North Atlantic.

The Laté 521 remained at Berre intact up until August 1944 when, following the launch of Operation Dragoon by the Allies to liberate southern France, the aircraft was deliberately destroyed by the retreating German occupying forces.