student at the Indonesian Army Command and General Staff College in 1964. Tambunan and Witono were both commemorated by the Indonesia-Australia Defence Alumni Association with the Sarsono–Tambunan Memorial Lecture Series held in Indonesia and Australia on a quarterly basis. On 1 November 1968, Tambunan was promoted as a colonel and became the chief of staff of the 1st Military Regional Command/Bukit Barisan, located in North Sumatra. He ended his term on 28 September 1971 and was replaced by Colonel SMT Hutagalung. He was transferred to Java, and in the same year he became the Deputy Governor of Educational Operations in the Republic of Indonesia Armed Forces Academy. In 1974, he was transferred to Sulawesi and became the commander of the 13th Regional Military Command/Merdeka on 25 February 1974 until 8 January 1976. After his term ended, he was transferred once again to Jakarta, and assumed office as the commander of the Indonesian Army Command and General Staff College from 3 March 1976 until 25 May 1978. Governor of North Sumatra On 12 June 1978, Tambunan was officially inaugurated as the Governor of North Sumatra by the Coordinating Minister for Political and Security Affairs Maraden Panggabean. The inauguration ceremony was held at the building of the Regional People's Representative Council of North Sumatra, and was attended by the Commander of the 1st Regional Defense Command G.H. Mantik. One of the main priorities during Tambunan's governorship was the creation of new subdistricts in North Sumatra. In 1981, Tambunan enacted a decree that adds 10 subdistricts in North Sumatra, specifically in Binjai, Pematangsiantar, and Sibolga. Further additions was enacted in 1982, when the administrative city of Kisaran and Padangsidempuan was formed. 5 new subdistricts were formed, with 2 subdistricts in Kisaran and 3 subdistricts in Padangsidempuan. Tambunan also formed the new post of assistant governor for the purpose of coordination, supervision, and decentralization. There were four assistant governors, each tasked with assisting the governor in four different regions. The region was centered in main cities of the province: Sibolga, Pematangsiantar, Medan, and Kisaran. In the agricultural sector, Tambunan enacted a decree for the special intensification and extensification (INSUS) for rice production. This decree was enacted to counter the low output of rice in North Sumatra at that time. The INSUS status was later upgraded to a full economic operation, named as the Operasi Desa Makmur (ODEMA, Operation Prosperous Village). Tambunan was also one