the Agreement, the interest of the air carriers of the other Government shall be taken into consideration so as not to affect unduly the services which the latter provides." Fares were made subject to regulatory approval by authorities in each country or by the International Air Transport Association, effectively giving the IATA immunity from US antitrust law, which immunity remained in effect on North Atlantic routes until 1979. Operations under the agreement 1940s Pan Am took delivery of the Lockheed 749 Constellation in June 1947 and began its "round-the-world" route with eastbound stops in New York, Gander, Shannon, London, Istanbul, Dhahran, Karachi, Calcutta, Bangkok, Manila, Shanghai, Tokyo, Guam, Wake, Midway, Honolulu and San Francisco, taking advantage of Bermuda Agreement fifth freedom rights. Newfoundland, an essential refueling stop on any transatlantic air route in the 1940s, was part of Britain at the time the Bermuda Agreement was signed. In 1949, following its accession as a Canadian province, the United States signed an agreement with Canada to provide for fifth freedom rights to and from Gander. 1950s Pan Am acquired AOA from American Airlines in 1950, concentrating the US-UK air travel market to three carriers: Pan Am, TWA and BOAC. BOAC, still Britain's sole transatlantic carrier, sought to compete with Pan Am's "round the world" service by offering an "all-red" route from Britain to Australia via Canada, but bilateral agreements between the UK and these countries stalled in the early 1950s. BOAC proceeded to open a London-Chicago route in May 1954, with the intention to extend the service to San Francisco and Tokyo. The San Francisco extension was not realized until 1957, and US government approval for the Tokyo service did not come until 1959 due to objections by Northwest Airlines. BOAC introduced de Havilland Comet jet service on the London-New York route in 1958. TWA began jet service on the New York-London-Frankfurt route in 1959. 1960s The United States began to exercise an even more dominant position in the transatlantic market during the 1960s. One key issue was that Pan Am and TWA began to use the hub and spoke system to feed passengers from many US destinations through a transatlantic "gateway" and on to Europe, giving the US carriers an advantage in serving secondary markets. Partly as a result of this competitive pressure, the market share of BOAC on transatlantic routes fell from 37.8% in 1961–62 to 30.9% by 1966–67.