On 4 March 1947, in Dunkirk, France and the United Kingdom sign a Treaty of Alliance and Mutual Assistance against a possible German attack. The Treaty enters into force on 8 September 1947.

At a meeting held in Paris on 17 October 1948, the Finance Ministers of Western Union emphasise the need to give the Brussels Treaty an economic content. They believe that questions relating to common defence should not be the sole aim of the cooperation, but that discussions on commercial questions should also take place.

Poster presenting the Western Union Cultural Identity Card, an initiative aimed at promoting cultural exchanges between the five Member States of the Brussels Treaty Organisation.

Convention on social and medical assistance aiming to extend cooperation between the Member States of Western Union in the social field. The convention was signed in Paris on 7 November 1949 and came into force on 27 April 1951.

On the beaches adjoining Weybourne Camp near Norwich, in the county of Norfolk in the United Kingdom, British gunners prepare to train the Belgian and Dutch troops of Western Union in anti-aircraft techniques.

Example of a questionnaire sent by the Agency for the Control of Armaments (ACA) to the Member States of Western European Union (WEU), in this case on the subject of armaments for naval forces in 1956.

In 1988 and 1990, during the Iran–Iraq and Gulf Wars, WEU carries out its first joint actions, in particular with the naval minesweeping operation Cleansweep in the Persian Gulf.

Robert Pontillon, President of the Assembly of Western European Union (WEU), and Armand De Decker, Chairman of the Liberal Group in the Assembly of WEU, as operations are carried out in 1991 in the context of the Gulf War.

On 10 July 1992, the Council of Ministers of Western European Union (WEU) decides that WEU’s naval forces will participate in monitoring the embargo imposed by the United Nations against the Federal Republic of Yugoslavia in the Adriatic (‘Sharp Vigilance’ and ‘Sharp Fence’ operations). In this context, the WEU and NATO Councils decide to implement a joint operation from June 1993 to June 1996, placed under a single command and known as Sharp Guard.

Between 1993 and 1996, in the context of the Yugoslav conflict and in coordination with the Organisation for Security and Cooperation in Europe (OSCE), Western European Union (WEU) provides police and customs assistance to Bulgaria, Hungary and Romania for the enforcement of United Nations sanctions on the Danube.