The United States invaded
Haiti in 1915 and occupied the country for 19 years. In the years following the initial invasion, rebel forces under Charlemagne Péralte conducted an armed resistance to the occupation. On the night of October 31–November 1, 1919, Hanneken assassinated the resistance leader, Péralte. Hanneken was disguised and was led into the rebels camp in Northern Haiti by Jean-Baptiste Conze, one of Péralte's officers who betrayed the Haitian leader. In the short skirmish that ensued, Hanneken killed Péralte and about 1,200 of his followers were killed, captured, or dispersed. Hanneken subsequently circulated a photograph of Péralte's half-naked body tied to a door. However, the attempt to intimidate backfired and instead evoked sympathy for Péralte. Hanneken was awarded the Medal of Honor for "extraordinary heroism" and "conspicuous gallantry and intrepidity in actual conflict with the enemy" and, in December 1919, commissioned as a
second lieutenant. In another raid just five months after the death of Charlemagne, he shot and killed Osiris Joseph, another Haitian rebel leader who succeeded Charlemagne. He was awarded the
Navy Cross for this act. Upon appointment as a second lieutenant he was assigned to train the Haitian police force, the
Gendarmerie. He was ordered to return to the United States in April 1920, and following his arrival at the Marine Barracks,
Quantico, Virginia, he was assigned to a special course at the Marine Corps Schools. ==1920s service and occupation of Nicaragua==