That same year Umar joined them as an undercover operative over Dhien's complaints, working his way up through the colonial military's ranks.

For his service, on 1 January 1894, Umar was given the title Johan Pahlawan and control of a legion of 250 fully armed soldiers.

[1] On 30 March 1896, Umar and his troops deserted, taking including 800 weapons, 25,000 bullets, 500 kilograms (1,100 lb) of ammunition, and 18,000 dollars.

Together with 400 soldiers under the command of Teuku Panglima Polem Muhammad Daud, Umar attacked the Dutch forces, killing 25 and injuring 190.

There are many streets named after him throughout Indonesia, including a main thoroughfare in the well-known suburb of Menteng in Jakarta, as well as a field in Meulaboh.