In early March, instructions were given by the British Fourth Army corps commanders, for advanced guards to maintain contact should the Germans retreat, with larger forces to follow and dig in behind them on defensible ground, so that the advanced guards could fall back if attacked. The first sign of a German retreat was seen on 14 March when fires were seen in St Pierre Vaast Wood. Later in the day, the British entered Saillisel and by 16 March, most of the wood had been occupied. The British Fourth and Fifth armies organised all-arms forces of cavalry squadrons, infantry and cyclist battalions and artillery batteries, some of which had armoured-car units attached. On 15 March the French (GAN), south of the junction with the British Fourth Army at Roye, was ordered to follow up a German retirement. By 18 March the German 6th, 1st, 2nd and 7th armies were withdrawing and British and French cavalry patrols met in Nesle, behind the old front line. When French troops entered Lassigny they caused a traffic jam and vehicles that tried to skirt the jam bogged in mud. GAN had been on ten-day's notice to attack (about fourteen days before (GAC) attacked on the Aisne) between the Oise and Avre rivers. News of the first German retirements led the army group commander, General Franchet d'Espérey to advocate an attempt to surprise the Germans and force them to retreat prematurely. The suggestion was rejected and GAN began to prepare a limited attack for 17 March, by when the Germans had gone.