The rank insignia worn by SS Major Klaus Kessler is that of Brigadeführer (Brigadier General) which was used on SS uniforms between 1940 and 1942, not that of Sturmbannführer (Major). The storyline is set during Operation Market Garden which was in 1944. Also because Kessler was an SS officer, the proper manner to which he would be addressed is "Herr Sturmbannführer", not "Herr Major".