SAAB, Kockums, Bofors and Hägglunds (today BAE Systems AB). Prime minister Olof Palme summarized Swedish neutrality in a speech in 1985: Vi står för Sveriges oberoende i fred och kommer med fasthet att värna vårt territorium mot varje inkräktare (en: We stand for Sweden's independence in peacetime and will, with firmness, defend our territory against every foreign intruder). In the early 1960s, US nuclear submarines armed with mid-range Polaris A-1 nuclear missiles were deployed outside the Swedish west coast. Range and safety considerations made this a good area from which to launch a retaliatory nuclear strike on Moscow. The submarines had to be very close to the Swedish coast to hit their intended targets; as a consequence of this, in 1960, the same year that the submarines were first deployed, the US provided Sweden with a military security guarantee. The US promised to provide military force in aid of Sweden in case of Soviet aggression. This guarantee was kept secret from the Swedish public until 1994, when a Swedish research commission exposed evidence of it. As part of the military cooperation, the US provided much help in the development of the Saab 37 Viggen, as a strong Swedish air force was seen as necessary to keep Soviet anti-submarine aircraft from operating in the missile launch area. In return, Swedish scientists at the Royal Institute of Technology made considerable contributions to enhancing the targeting performance of the Polaris missiles. Population change Since 1930, emigration has been slight. About 15,000-30,000 people left Sweden annually after 1965. Sweden welcomed refugees and displaced persons at the end of World War II. Because of the low birth rate, immigration accounted for 45% of population growth between 1945 and 1980. Aliens may vote in Swedish local elections after three years of legal residence. Sweden became highly urbanized after World War II, reaching 83% urban in 1990. As recently as 1940 only 38% of the population lived in urban areas, and in 1860, before industrialization, the proportion was only 11%. Large-scale movement from the countryside to the United States ended about 1900. Since 1945 the movement to Swedish cities has accelerated and has brought about a population decline in many areas, especially in the north. Most cities are small. Only 10 cities have populations of more than 100,000. The Stockholm metropolitan areas has a population of 2 million; Gothenburg has 906,000 in its metropolitan area and Malmö