During the Operation Product and Operation Kraai launched by the Dutch to invade North Sumatra, the North Sumatra branch of Indonesian Christian Party formed the Arrow Division. The division was headed by Siregar as a titular colonel, codenamed Partahuluk Raso (). Several personnel were originally his student or would become his student. Originally, the HQ of the division was in Pematang Siantar, but later moved to Muara. Together with his friend Bosar Sianipar, code named "Mondar Mandir" (), Siregar and him became one of the most wanted figures by the Dutch Army. The division was widely popular in Pematang Siantar due to the divisions' all out defense against the massive Dutch army that managed to broke through the fortifications of Medan Area Lembung.