total of 314 air raids on Berlin, with 85 of those coming in the last twelve months. Half of all houses were damaged and around a third uninhabitable, as much as 16 km² of the city was simply rubble. Estimates of the total number of dead in Berlin from air raids range from 20,000 to 50,000; current German studies suggest that a figure in the lower part of this range is more likely. This compares to death tolls of between 25,000 and 35,000 in the single attack on Dresden on 14 February 1945, and the 42,000 killed at Hamburg in a single raid in 1943, with both the Hamburg and Dresden raids combined having a lower casualty total than the 9/10 March 1945 Operation Meetinghouse single firebombing raid on Tokyo, devastating some causing the loss of at least 100,000 lives in the Japanese capital. Berlin's defences The Nazi regime was well aware of the political necessity of protecting the Reich capital against devastation from the air. Even before the war, work had begun on an extensive system of public air raid shelters, but by 1939 only 15% of the planned 2,000 shelters had been built. By 1941, however, the five huge public shelters (Zoo, Anhalt Station, Humboldthain, Friedrichshain and Kleistpark) were complete, offering shelter to 65,000 people. Other shelters were built under government buildings, the best-known being the so-called Führerbunker under the Reich Chancellery building. In addition, many U-Bahn stations were converted into shelters. The rest of the population had to make do with their own cellars. In 1943, the Germans decided to evacuate non-essential people from Berlin. By 1944 1.2 million people, 790,000 of them women and children, about a quarter of the city's population, had been evacuated to rural areas. An effort was made to evacuate all children from Berlin, but this was resisted by parents, and many evacuees soon made their way back to the city (as was also the case in London in 1940–41). The increasing shortage of manpower as the war dragged on meant that female labour was essential to keep Berlin's war industries going, so the evacuation of all women with children was not possible. At the end of 1944 the city's population began to grow again as refugees fleeing the Red Army's advance in the east began to pour into Berlin. The Ostvertriebenen ("refugees from the East") were officially denied permission to remain