Before proceeding to the battle itself there is one further point to which we desire to refer, and that is the thick fog which lay over the marshes of the Oise early on the morning of the 21st and the succeeding days. The effect of this fog on what transpired had been variously estimated. The general consensus of opinion of officers and men who took part in the battle is that it was a great disadvantage to the defence. In many ways this was undoubtedly the case. The complete blotting out of all landmarks beyond a few yards' radius rendered any sort of co-operation with adjoining units impossible; the inter-supporting machine-guns between the redoubts were comparatively useless for they could not see when and where to fire. The artillery was also handicapped for it knew not where to lay its barrages to trap the advancing enemy. Many times in the course of the battle, redoubts which thought themselves not yet attacked suddenly realised that in the fog they had been surrounded and cut off. The general result was that the defence degenerated into a series of isolated battles in which companies and platoons made individual stands, unsupported by their comrades and in ignorance of what was occurring on their flanks. But there is another side to the picture, and the German opinion is equally strong, that but for the fog their success would have been more far-reaching than it actually proved to be. The inevitable loss of direction and touch between attacking columns, the feeling of uncertainty born of drifting forwards without seeing one's surroundings, the strange tricks which fog always plays in the matters of distance and sound--all these could not but affect detrimentally the speed and cohesion of the attack--and speed was of all things the essential for complete German success. Swiftly though the attack came, from the very first day the advances were made far behind schedule, and to this extent the German attack failed. How far it failed through the fog we will not venture to estimate; but that the fog was a contributory factor there can be no doubt. On the afternoon of the 20th March the order "Prepare for attack" was received from III Corps, and by 3.30 p.m. all companies of the Battalion were ready to man their battle positions. The scheme of defence has already been alluded to in general terms, and it has been indicated that both the Forward and Battle Zones were divided into a series of defended localities each held by a company. These localities comprised a main keep, supported by two or more subsidiary redoubts, while the space intervening between adjoining localities was covered by the guns of the Brigade Machine-Gun Company. [Illustration: THE RETREAT FROM LA FÈRE, MARCH 1918] Map No. 15 shows the relative positions of the various localities in the scheme of defence, and in the Northern Brigade area, with which alone we are henceforward concerned, the disposition of troops on the night 20th/21st March was as follows: