Military coup means the sudden overthrow of a government illegally by military. When the military coup is despotic or the person who leads the military coup is despotic, then it is called the dictatorship of military coup.
For example : a military coup took place in Chile on 11th September 1973. The coup was led by General Augusto Pinoshet, who was a dictator.
So this is called the dictatorship of military coup.