[1] Wærn is one of only two Swedish officers (the other being Brigadier General Jan-Gunnar Isberg) who have served as brigade commanders in combat under the auspices of the United Nations.

After his service in the Congo, he continued his career in various roles, including commander of the Swedish UN Battalion in Cyprus.

He chronicled his experiences in books such as Katanga and Cyprus, which contributed to his recognition as a significant military figure in Sweden.

Wærn served as deputy military attaché in Copenhagen in 1948 and as second teacher at the Swedish Infantry Combat School the same year.

He was first teacher at Infantry Combat School in 1957 and the same year he was appointed ADC to King Gustaf VI Adolf.

[7] At the same time, he was brigade commander of the Swedish, Indian and Irish troops in southern Katanga, which was part of the United Nations Operation in the Congo (ONUC) from June 1961 to May 1962.

[6] Bo Pellnäs wrote the following about Wærn: "At its core, Wærn's leadership was characterized by words of wisdom uttered in China over four thousand years ago: 'Regard your soldiers as your children, and they will follow you into the deepest valleys; look on them as your own beloved sons, and they will stand by you even unto death'.

[12] In spring 1998, the TV program Röda rummet [sv] did a viewing poll about the century's most significant Swedish books.