 Having been equipped with more powerful engines, the Laté 521 conducted a further four return flights to New York between May and July 1939.During one of these, pilot Henri Guillaumet flew from New York City to Biscarrosse at an average of 206 km/h (127 mph), including with one engine out.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 E.6 flotilla, based in Port-Lyautey, Morocco, where they were used to perform maritime patrol missions in the North Atlantic.