Early in the morning of May 10, 1940, Rotterdam was transformed into a sea of flames by the German bombardment. 900 inhabitants of the city were killed, 78,000 people were made homeless, and 260 hectares (642 acres) of land was destroyed. When the Germans threatened to destroy other cities, the Dutch surrendered on May 15, 1940.
German troops in the east of the Netherlands crossed the Dutch-German border. At the same time, German airborne troops landed in the west of the Netherlands. The country was taken by surprise; there was chaos and panic, but the military resistance in some places was stronger than the Germans had expected. They began to fall behind schedule, and something had to be done to crush the Dutch resistance as quickly as possible. In the early afternoon of May 14, the Rotterdam garrison commander was given an ultimatum to turn over the city. Should he refuse, the Germans would completely destroy it. The Dutch did not answer the ultimatum with a yes or a no, but instead sent the documents back requesting that they be signed and that the German sender’s name and rank be stated. In response, a new ultimatum was issued which would expire in several hours. But the Germans did not await the Rotterdam garrison commander’s reply. Planes were already on their way from Germany. At 1:25 p.m., the first bombs were dropped. In a matter of minutes, Rotterdam was transformed into a sea of flames.
Source: Nederland en de Tweede Wereldoorlog ["The Netherlands and WWII"], comp. René Kok and Erik Somers, NIOD; Uitgeverij Waanders, 2005