During World War II, Liberia became strategically important to the United States because of its position on the South Atlantic air ferry route and its rubber production. In July 1941, Pan American Airways began developing an airfield at Harbel, Liberia, under an arrangement with the U.S. War Department. The field was planned as an alternate South Atlantic landing point for aircraft being ferried to British forces in the Near East, and Pan American hired the Firestone Company to perform the construction work. The runway was built long enough for B-47 Stratojet bombers to land for refueling, giving Liberia what was for many years the longest runway in Africa. U.S. President Franklin D. Roosevelt had lunch with President Edwin J. Barclay at Roberts Field during his visit to Liberia in January 1943. From 1943 to the end of World War II in 1945, Roberts Field Airport, as it was then known, served as an alternative base for a contingent of 26 Squadron SAAF which flew Vickers Wellington bombers on anti-submarine (U-Boat) and convoy escort patrols over the Atlantic. Their main base was at Takoradi, in the Gold Coast. The story of Roberts Field is consistently intertwined with the history of Pan American World Airways. In fact, from the end of World War II until 1985, the airport was administered and operated by Pan American under contract with the Republic of Liberia's Ministry of Transport. Monrovia was consistently a key link in Pan American's African network, usually an intermediate stop between Accra and Dakar, from which service continued onward to Europe and New York. In the late 1970s and into the early 1980s, the airport became Pan Am's principal African hub, with a nonstop Boeing 747 service from New York JFK connecting at Robertsfield to such destinations as Dakar, Accra, Abidjan, Lagos, and Conakry, among others, and continuing on to Nairobi and even at times Johannesburg, so that for many years virtually every Pan Am passenger to Africa passed through Robertsfield. Pan Am's presence diminished during the 1980s, as Pan Am's African network was slowly pulled down. Pan Am ended its management of the airport in 1985 but as late as 1986 the airport was still a stop on the JFK-Dakar-Monrovia-Lagos-Nairobi route. By 1987, Pan Am was no longer serving Monrovia at all. A number of European airlines also served the airport from the mid-1960s to the mid-1980s, including British Caledonian Airways with Boeing 707s, KLM Royal Dutch Airlines with Douglas DC-8s and Sabena, Swissair and UTA with these three air carriers all operating McDonnell Douglas DC-10s into Robertsfield. Scandinavian Airline System also served Monrovia, from Copenhagen. In the mid-1970s this service consisted of a weekly flight via Düsseldorf and Madrid and a second weekly flight via Zürich, then onward to South America: Rio de Janeiro, Montevideo, and Santiago de Chile. Similarly, VARIG employed RIA as a stop on its flights between Brazil and Europe, which began in the mid-1960s and lasted at least until the mid-1970s, with various routings including Rio de Janeiro-Monrovia-Rome and Rio-Monrovia-Madrid-Rome. VARIG's Flight between Rome and Rio crashed at Monrovia in March 1967, and remains the worst aviation accident in Liberia to this day. As with Pan Am, several African flag carriers utilized Robertsfield as a waystation on transatlantic routes. As early as 1966, Nigeria Airways began a codeshare cooperation on Pan Am's flights to New York-JFK from Lagos via Monrovia, and in later decades Monrovia remained a stop on its weekly services to New York, at most times utilizing its own McDonnell Douglas DC-10. This also included for a time a weekly Monrovia-Port of Spain-Miami flight. Until 1983, Air Afrique's DC-10s also stopped at Robertsfield on that airline's Abidjan-Monrovia-Dakar-New York services. In April 1988, Zambia Airways commenced service from Lusaka to New York via Monrovia.