Source: adapted from B. Graham (1995) Geography of Air Transport, Chichester: Wiley.
Due to range limitations, the first international air routes were composed of a series of refueling stages. Crossing the comparatively calm and narrow South Atlantic was much easier than transiting the North Atlantic. Although the world’s most powerful economies bracketed the North Atlantic, regular air services between the United States and Europe did not begin until 1939, when Pan Am offered Boeing 314 flying boat services. Air travel was highly expensive and only used by a few wealthy individuals or high-ranking officials. For instance, the 9-day trip from London to Sydney on Imperial Airways in 1938 included overnight stays at luxurious hotels along the way and cost more than $15,000 in 2000 dollars. Following the outbreak of World War II, commercial services were suspended but military flights operated by Pan Am and other carriers continued, providing experience and stimulating technical advances upon which the postwar expansion of aviation would be based.