The retirement began at 10-30 p.m., being covered by small rearguards. In the darkness the troops were not seriously pressed by the Germans. Long before dawn all battalions were established in their new positions, the three Brigade Headquarters of the 36th Division being at Lavesne, and that of the 61st Brigade in the old Divisional Headquarters at Ollézy. General Nugent had meanwhile transferred his headquarters to Estouilly, north of Ham. It must be remembered that each Brigade had by now had one battalion almost completely destroyed, and that the Battle Zone battalions were at an average strength of about two hundred and fifty men. There was an accretion in artillery strength. Two batteries, A/91st and C/91st, of the 20th Divisional Artillery, together with the 232nd Siege Battery, were put at the disposal of the 36th Division, and remained with it throughout the retreat, though there were constant changes in the formation of Groups. The Siege Battery was later transferred to a special Heavy Artillery Group, with two others, directly under the orders of the 36th Divisional Artillery. The destruction of bridges and pontoons allotted to the Engineers of the 36th Division was carried through without hitch. Shortly after noon the pontoon and foot-bridge at Fontaine were destroyed by the 121st Field Company, which in the small hours of the 22nd of March blew up the whole group of bridges between Grand Séraucourt and Le Hamel. Later, in daylight, the 150th Field Company blew up the Artemps Group. The Tugny and St. Simon bridges had been allotted to other sections of the company. Lieutenants C. L. Knox and J. B. Stapylton-Smith were each responsible for twelve bridges. The first warning received by the former was when the débris of the Artemps bridges floated down-stream. He at once commenced his task. Several of the bridges were destroyed under machine-gun fire. At Tugny, the Germans were advancing on the main steel-girder bridge when the time-fuse failed. The night dew or the mist had spoiled it. As Lieutenant Knox rushed forward the foremost of the enemy were upon the bridge, a long one. He tore away the useless time-fuse, clambered under the frame-work of the bridge, and lit the instantaneous fuse. The bridge was destroyed, and, by some miracle, Lieutenant Knox was uninjured. He received the Victoria Cross. Among many heroic actions performed by officers and men of the Division in the course of the war it would be difficult to point to one of finer calibre. At St. Simon, Lieutenant Stapylton-Smith blew up a large number of the enemy with one of the three main bridges.