replaced by the fourth Colijn cabinet on 24 June 1937. In October 1938 Oud was nominated as Mayor of Rotterdam, and he announced his resignation as Leader and Parliamentary leader, endorsing his long-serving deputy Dolf Joekes as his successor. Oud resigned Leader and Parliamentary leader the day he was installed as Mayor, taking office on 15 October 1938. On 14 May 1940 the Luftwaffe destroyed almost the entire historic city centre of Rotterdam during the German invasion, leading the Dutch government to capitulate the next day. On 10 October 1941 Oud resigned in protest against the German occupation and was briefly detained in the Ilag Sint-Michielsgestel in the summer of 1942. During the rest of the German occupation Oud wrote dozens of books on history and politics. Following the end of World War II, Oud was again appointed as Mayor of Rotterdam, taking office on 7 May 1945. On 9 February 1946 the Free-thinking Democratic League (VDB), the Social Democratic Workers' Party (SDAP) and the Christian Democratic Union (CDU) chose to merge to form the Labour Party (PvdA). Oud was one of its co-founders, but left the party a year later, after which he and several other former members of the Free-thinking Democratic League formed the rump party Committee-Oud in February 1947. On 24 January 1948 the Committee-Oud and the Freedom Party (PvdV) chose to merge to form the People's Party for Freedom and Democracy (VVD). Oud became the first Leader of the People's Party for Freedom and Democracy. For the 1948 election, Oud was the lijsttrekker (lead candidate) of the People's Party for Freedom and Democracy. The party had six seats in the House of House of Representatives previously held by the Freedom Party and won two additional seats, now having eight seats in the House of Representatives. Oud again returned as a Member of the House of Representatives and became the party's first Parliamentary leader on 27 July 1948. The following cabinet formation resulted in a coalition agreement between the People's Party for Freedom and Democracy, the Catholic People's Party (KVP), the Labour Party and the Christian Historical Union (CHU) which formed the Drees–Van Schaik cabinet, with Oud opting to remain in the House of Representatives instead of filling a ministerial post. Oud also served as Chairman of the People's Party for Freedom and Democracy from 8 April 1949 until 9 November 1963. Oud served continuously as Leader