Knud Børge Martinsen (30 November 1905 – 25 June 1949) was a Danish officer and the third commander of Frikorps Danmark.

[citation needed] The Occupation of Denmark on 9 April 1940 was a big shock to him, but on 26 April 1940 he joined the Danish National Socialist Workers' Party of Denmark (DNSAP) and took part of several demonstrations in his uniform which ended up in his military papers and prevented further career advances.

Actually Martinsen was temporarily commander of Frikorps Danmark between Kryssing's resignation and von Schalburg's appointment.

In October 1944 Martinsen was relieved from his position and then arrested and imprisoned in Gestapo's prison in Berlin.

One of the murders was the shooting in March 1944 in the headquarters of the Schalburg Corps of a fellow member, Fritz Henning Tonnies von Eggers, whom Martinsen believed had committed adultery with his wife.