During World War I, the union was largely inactive, but it was revived in 1919, and created a new section for ships' stewards.
[1] The union was successful in the early 1920s, and in 1925 was able to fund the construction of a sanatorium, De Mick.
During World War II, the union was forced to stop activity in the Netherlands, but a few leaders including Omer Becu escaped to the United Kingdom and were able to keep the union running from there.
[1] In 1947, the Belgian Union of Tramway and Municipal Transport Workers merged into the union, and immediately became its largest sector, just ahead of its port membership, but it split away again in the early 1950s.
[1][2] As of 2011, the union has two sections: Ports, Road Transport and Logistics; and Maritime.