Using this windfall and other sources of information , the French adapted Plan '' XV '' in 1906 , to be ready for a German invasion of Belgium and subsequent plans contained increases in the forces to be assembled to the north and north - east of Verdun .
Using this windfall and other sources of information , the French adapted Plan XV in 1906 , to be ready for a German invasion of Belgium . 
 Subsequent plans contained increases in the forces to be assembled to the north and north - east of Verdun .