Listers production was partly turned over to the manufacture of arms in World War I.

At one time the navy gave Mikael Pedersen the use of a warship to try out improvements to cannons which he had suggested. Nothing came of this before the war was over but his ideas were used in cannon production later.

There was another invention that Mikael Pedersen had great success with, this was a very accurate instrument for controlling dimensions on ammunition for rifles and cannons. Mikael Pedersen and Ingeborg's war effort was highly respected in the town. It amused Mikael Pedersen and many others, when he was suspected of spying for the enemy because the nurse in the house was a German.

The police kept Mikael Pedersen under observation for some time but they often had great difficulty in following him. Mikael Pedersen and his Danish colleagues were riding bikes with 3-Speed gears, so the police gave up the chase.

Cycle production fell gradually and was partly taken over by other companies round about in Gloucestershire. Licence fees to Mikael Pedersen remained unpaid, and with his lack of sense for business, he was often cheated out of other payments.

Another problem was his increasing alcohol misuse and his marriage was not going well. Ingeborg had bought a factory just outside Dursley where instruments of Mikael Pedersens design were produced. She did this in order to keep herself and the children as Mikael Pedersen never had any money to support his family. In 1918, Ingeborg left Dursley with the children and moved to London, her instrument production ceased, and she lost almost all her savings so that she was dependent on help form her family in Denmark.

Mikael Pedersen had developed a cancerous tumour above his right eye, which was operated on, but this didn't have any effect on his way of life. He disappeared one day and for a couple of years nobody knew what had become of him; his time in Dursley had come to an end.

The house in Dursley was sold with all its contents and Ingeborg went back to Denmark where she lived with the family at Stege-Lendemark. She married the editor Jens Kristoffer Jensen, and the boys changed their surname to Jensen.

Ingeborg did everything to forget Mikael Pedersen and it wasn't allowed to mention his name among the family. Later there simply arose a trauma, among the children and grand-children, as to who this grandfather Mikael Pedersen was and what had become of him.

Ingeborg had taken over the house at Marbjerg that had stood empty for many years. During the war it had been requisitioned for the use of conscripts to the security force, who found all Mikael Pedersens furniture and wooden models suitable for firewood during the cold winter months. Ingeborg sold the house later and bought a house in Holte, north of Copenhagen, where she moved, together with her sons.