- Not to be confused with contemporary German painter Karl Hofer (1878-1955)
Retired, as "Generalleutnant a. D.", Höfer defended German Upper Silesia against Polish insurgents in the Silesian Uprisings in 1921. The Freikorps leaders had agreed upon Höfer as commander; he led them to success in the Battle of Annaberg. In the international press, he was referred to as "General Hoefer" or "Teuton Commander Hoefer".
- Karl Hoefer: Oberschlesien in der Aufstandszeit, 1918-1921: Erinnerungen und Dokumente, published by E.S. Mittler & Sohn, 1938, 376 pages
- reviewed by H. F. P. Percival, International Affairs (Royal Institute of International Affairs 1931-1939), Vol. 17, No. 6 (Nov. - Dec., 1938), pp. 853–854 (review consists of 2 pages)
- Andreas Dornheim: Röhms Mann fürs Ausland
- The German Freikorps 1918-23, By Carlos Caballero Jurado, Ramiro Bujeiro
- The New York Times June 27, 1921, Monday Page 1, 829 words 
- Karl Hoefer (1938). "Oberschlesien+in+der+Aufstandszeit,+1918-1921"&lr= Oberschlesien in der Aufstandszeit, 1918-1921. E.S. Mittler & sohn.
- . JSTOR 3019448. Missing or empty
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