During World War II the company was affected by the German occupation: in 1941 Vereinigte Stahlwerke had acquired 40% of the company from the shareholdings of the state and city of Amsterdam. The directors of the company Housz and Holtrop went into hiding in 1943. The mouth of the North Sea canal at IJmuiden was used as a base for the Kriegsmarine, and the steelworks itself was a strategic target for attack, and bombings and lack of raw materials brought production to a halt.