Bochum was first bombed heavily in May and June 1943. On 13 May 1943, the city hall was hit, destroying the top floor, and leaving the next two floors in flames. On 4 November 1944, in an attack involving 700 British bombers, the steel plant, Bochumer Verein, was hit. One of the largest steel plants in Germany, more than 10,000 high-explosive and 130,000 incendiary bombs were stored there, setting off a conflagration that destroyed the surrounding neighbourhoods. An aerial photo shows the devastation.