Jung led the work on a comprehensive book about Sweden's war history, conducted extensive archival research, and played a key role in defence policy discussions.

He held this position until 1951 and played a crucial role in shaping the future organization of the Swedish defence post-World War II.

Despite facing challenges and opposition, Jung's determination and strategic leadership left a lasting impact on the Swedish military, modernizing its defence and anchoring it among the people.

Historians describe Jung as a complex figure with both tactical cunning and a commitment to strengthening Sweden's defence.

[6] During this time, Jung took an instructor course at the Royal Central Gymnastics Institute from 1907 to 1908,[5] and served as company commander in 1st Division's (I. arméfördelningen) volunteer school in Halmstad from 1908 to 1909 and from 1909 to 1910.

[3] The Defence Act of 1925 with its extensive downsizing of units and personnel, left its mark on Jung's generation of officers and instilled in many paralysis of action.

In this situation, Jung deservedly took the lead for those who did not want to give up the fight for a modern defence with a broad base and adapted to society's resources.

During his service in the War History Department, he gathered around him a group of younger talented army officers for a debate on defence issues[8] and eventually founded Ny militär tidskrift ("New Military Journal") in 1927,[9] whose editor he was 1927–1930.

[7] On 31 December 1943, Jung was promoted to lieutenant general from 1 January 1944 and was appointed Supreme Commander of the Swedish Armed Forces for six years from 1 April 1944.

[22] During this time he was against the Swedish extradition of Baltic soldiers in 1945 and a friend of NATO, as his speech to students at Lund University in November 1949 shows.

[23] About his other activities as Supreme Commander, an obituary read: "Jung's work became very important in order to present a plan for the Swedish Armed Forces's future organization after World War II.

With indomitable energy, Jung succeeded in gaining the attention of the Swedish government for his proposals and in preventing the ruling organization from collapsing.

It has been said by the former Supreme Commander, General Stig Synnergren that ’the modernization and anchoring of the defence among the Swedish people is Jung's lasting effort’.