The Klingon Defense Force, abbreviated KDF, was the military branch of the Klingon Empire.
As of 2373, the headquarters of the Klingon Defense Forces had been relocated to Ty'Gokor. The majority of Defense Force members were common warriors. In order to become an officer, a candidate had to pass the entrance exam. The prospective officer then had to be approved by an oversight council who could also reject the application. Officers usually served on the Klingon Empire's ships, and warriors were sent into battle, whether it be on planetary assaults or when boarding other vessels.
The system of hierarchy aboard ships within the Defense Forces was highly structured. According to one of their systems, one that had operated successfully for centuries, the first officer of any Klingon vessel had the duty to assassinate his captain when and if the captain became weak or unable to perform. It was expected that his honorable retirement should be assisted by his "first". The second officer also shared similar duties with his "first".