The original Aufmarschanweisung N°1, Fall Gelb (Campaign Instruction No 1, Case Yellow), was a plan to push the Allied forces back through central Belgium to the Somme river, in northern France, with similarities to the 1914 campaign of the First World War.[1] On 10 January 1940, the Mechelen Incident occurred, when a German aircraft carrying documents with parts of the operational plans for Fall Gelb crashed in Belgium, prompting another review of the invasion plan.