In 1948, PA had just introduced the ultra-luxurious Boeing 377 Stratocruisers to serve alongside DC-4s and DC-6s. Pan Am's U.S. domestic services allowed no local traffic but PA and it's subsidiaries did operate local service in Columbia, Brazil, Bolivia, Mexico, Columbia, and Ecuador. "The chosen instrument" operated the most extensive route structure in the world with TWA and American Overseas minor competition. In 1950, PA purchased AOA from American giving it a monopoly on international routes with TWA for 20 years. The flying boats were retired with a Boeing B-314 conducting the final flight in 1946.