»The air raid warning came at 10:57 a.m.«
Memorandum main engineering office, 1944

The German Reich began World War II in 1939, bringing with it the disastrous consequences we are all familiar with – also for the company in Darmstadt. Two years later, nearly 1,000 employees were drafted as soldiers. Like all other relevant companies in the country, the company was required by the government to hire women, forced laborers, and war prisoners to manufacture war-related products.

With the increasing air raids by the Allies, the fighting breaks into civilian life. By the end of the war in 1945, the city Darmstadt had endured 1,567 air raid warnings and 35 bombing attacks. The worst bombing attack on Darmstadt took place on the night of September 11 to 12, 1944, when 221 bombers from the Royal Air Force dropped 191 aerial mines, 33 explosive bombs and 285,848 stick-type incendiary bombs on the city. During this area bombing campaign, known as »Brandnacht« (the night of fire), more than 11,000 people suffocated and burned to death, a fifth of them children. The site premises, situated in the north of Darmstadt, were not hit at all by this air raid. Following the attack, the company helped as much as possible, organizing emergency accommodation for employees whose homes had been destroyed and procuring food.

The largest air raid on Darmstadt – measured by the formation size (458 aircraft) and the payload dropped – took place at noon on December 12, 1944. Some 4,128 explosive bombs (500 pounds) and more than 200 metric tons of incendiary bombs were dropped on the rail facilities and industrial operations in the north of the city, killing 303 people and injuring 78 more. The company was also severely affected by this heavy air raid: A total of 214 explosive bombs hit the site premises, killing 60 people. The attack destroyed 41% of the factory buildings and damaged a further 27%. Mountains of debris were everywhere, mixed together with production residues, all kinds of raw materials, countless chemicals, and solvents.

American forces occupied the company and Darmstadt on March 25, 1945. This marked the end of World War II for the company and the city.​ 

In 1945, it is time to clean up and to get production going again. Instead of trucks, horses and oxen are used. After the currency reform of 1948, the company must take out substantial loans in order to resume operations. The train station at the company is cleared of debris and ready for goods transports. In 1952, the company products are sent by plane to Japan.

The company commitment to providing company-owned apartments, dating back to the 19th century, is very important. There is a shortage. New apartment buildings are going up all over the city, and construction must be economical. Employees help themselves to overcome the housing shortage, despite the lack of capital.

In 1947, export business starts picking up again. E. Merck, Darmstadt, Germany, participates in the export trade fair in Wiesbaden, among other events. More than 50 employees work in this area in 1950. Joint outings offer a break from the work routine. In 1947, DINIE takes over all foreign companies in Argentina. The company is able to reacquire its subsidiary there in 1958.