Maxse's XVIII Corps also took part in Fifth Army's defence against the German Spring Offensive, beginning on 21 March 1918. At 10.45am on 22 March Gough issued written orders to corps commanders to retreat, if heavily attacked, to the forward line ("the Green Line" in front of the Somme – in practice little more than a line of signposts and wire) of the Rear Zone. Fifth Army staff also informed corps commanders of the impending French reinforcement and Gough's hopes to withdraw III Corps to form a reserve. On receiving these messages at around noon, Maxse ordered XVIII Corps to withdraw immediately, without cover of artillery fire, and they fell back behind the Somme altogether that evening. Gough attempted to halt Maxse's withdrawal when he heard of it, but it was too late. Watts XIX Corps on Maxse's left also had to fall back.