At the start of World War II, Lembong was an NCO in the Dutch colonial army (KNIL) in Manado.

[1]: 107  Lembong and several others were able to escape captivity and join a local guerrilla unit that was part of the USAFFE LGAF.

[2]: 67 After the war, Lembong returned to Indonesia as KNIL officer in January 1946 and later joined an irregular armed organization called the "Loyalty of the Indonesian People from Sulawesi" (Indonesian: Kebaktian Rakjat Indonesia Sulawesi (KRIS)) after Operation Product on 21 July 1947.

During Operation Kraai, Lembong was captured in Yogyakarta and jailed by the Dutch for a time in Ambawara.

[5]: 141 Lembong was initially considered for the Military Attaché position in the Philippines, but was instead appointed head of the Army Education Department.