Before World War II, Warouw was part of the Dutch colonial army (KNIL). After the war and upon the proclamation of Indonesian independence, Warouw was involved in organizing and became deputy leader of the "Republic of Indonesia Youth of Sulawesi" militia () in Surabaya. This group was also known as the "Loyalty of the Indonesian People from Sulawesi" () in Surabaya. This group was mostly made up of men from the Minahasa region in North Sulawesi who were residing in Java. Warouw took part in the Battle of Surabaya and emerged as a young military figure who showed valor during the battle. Starting from 1946, Warouw was assigned several military positions including Chief of Staff of the 6th Division of the Sea Army of the Republic of Indonesia () in Lawang and Chief of Staff of Base X of the TLRI in Situbondo. In 1948, he was appointed Deputy Commander of the 16th Brigade (Brigade XVI) and would subsequently succeed Adolf Lembong as commander of the brigade.