Gwenn ha Du (Breton for "white and black") was a paramilitary group founded at the end of 1930 in Paris by Célestin Lainé.
In July 1932, Gwenn ha Du decided to destroy a monument it found particularly offensive: a statue created by Jean Boucher marking the union of Brittany and France in 1532.
On August 7, the group claimed responsibility for the attack, which was intended to coincide with the 400th anniversary celebration of the union, taking place in Vannes under the guidance of French prime minister Édouard Herriot.
L'Humanité, the French Communist Party newspaper, spoke out the day after, protesting that Herriot didn't mention that all Celtic civilisation was wiped out, the refusal to acknowledge the Breton language and culture.
On November 20, Gwenn ha du members detonated a bomb on the railway line between Ingrandes and Champtocé, not long before Édouard Herriot's arrival there.