He was seconded to the Military Cartographic Institute, used by the Belgian state to make soldiers available to King Leopold II's private colony.

[1] He was assigned to the Fort de Shinkakasa, designed to protect the lower Congo, and completed the work on this structure.

[2] Moulaert criticized the Catholic Church's fermes-chapelles (farm chapels), mistreatment of the Congolese, seizure of land and failure to pay taxes.

[1] In May 1914 Moulaert requested a second ten-year term in the colony, which was granted on 1 August 1914, a few days before the start of World War I (1914-1918).

As commander of the Upper Congo Navy he organized and directed, from Léopoldville, the Belgian military expedition with the steamer Luxembourg which joined with the French in the Sangha operations in the Kamerun campaign against the Germans.

In December 1914 he asked to be reinstated in the Belgian army so he could fight in Europe, petitioning the king directly, but was refused.

In Léopoldville he argued about river and port infrastructure policy with his superior, the acting governor general Eugène Henry, and earned a reprimand.

This was the haven for the small flotilla that won the Battle for Lake Tanganyika, and was the nucleus of the future city of Albertville.

[2] Moulaert again became involved in controversy when he fell out with Geoffrey Spicer-Simson, commander of the British forces on the lake, and with his own seniors.

[2] On 20 August 1917, while he was serving on the Yser front Moulaert was appointed deputy governor general of the province of Équateur.

[3] At the end of 1919 Louis Franck, the Minister of the Colonies, gave Moulaert responsibility for the state mines at Kilo and Moto.

[2] Moulaert tackled improvements to roads, transport, medical support, supplies and crops, as well as mining installations, exploitation of alluvium and eluvium deposits, prospecting and research.

[2] In 1924 Moulaert returned to Brussels on a visit, and was appointed secretary general of a commission to examining the colony's transport.

In 1926 the Régie industrielle des Mines d’Or de Kilo-Moto was converted to a Congolese limited liability company.

[2] Moulaert boosted gold production at Kilo-Moto, but his methods were questioned, particularly forced recruitment of Black workers, who totaled 10,012 in 1918 and over 40,000 in 1939.

In 1935 Moulaert visited Kalima, where mining was just starting, and drew up plans for offices, houses, a hospital and workers camps.

[2] In the late 1930s Rodolphe Dufour, commissioner of Stanleyville Province, was the target of concerted and virulent attacks from La Belgika and the Kilo-Moto Gold Mines delivered by their influential representatives André Gilson, also president of the Association of Belgian Colonial Interests, and by Moulaert.