After the French surrender in Europe, tension developed along the border with Siam (now Thailand). These flared into hostilities between Siam and Vichy France in December 1940. In January 1941, "Lamotte-Picquet" became the flagship of a small squadron, the "Groupe Occasionnel". It was formed on 9 December at Cam Ranh Bay, near Saigon, under the command of "Capitaine de Vaisseau" Bérenger. The squadron also consisted of the colonial sloops "Dumont d'Urville" and "Amiral Charner", and the older sloops "Tahure" and "Marne". The "Groupe Occasionnel" with "Lamotte-Picquet" at its head, met a Thai squadron of two torpedo boats and a coastal defence ship in the Battle of Koh Chang on 14 January 1941. The Thai squadron was defeated, with both torpedo boats sunk and the coastal defence ship run aground. The victory was for naught, however, as the Japanese forced a settlement in the Franco-Thai War in favour of the Thai. Apart from a visit to Osaka, Japan in September 1941, "Lamotte-Picquet" was thereafter restricted in her activities.