Due to his reputation for bravery, Modu began to gather a group of extremely loyal warriors. He invented a signaling arrow that made a whistling sound in flight, and trained his men to shoot in the direction of the sound in synchrony. To be sure of his men's loyalty, Modu ordered the warriors to shoot his favourite horse, and anyone who refused were executed. He later repeated this test of loyalty, but with one of his favourite wives, and once again executed those who hesitated to obey his order. After he was sure of the absolute loyalty of his remaining warriors, he ordered them to shoot at his father during a hunting trip, killing him in a shower of arrows. With none of his followers failing to shoot at his command and the removal of his father, Modu proclaimed himself Chanyu of the Xiongnu.