that, The OHL reserve was down to one division and that the Germans would have to begin milking divisions for reserves, which led Haig and Rawlinson to believe that attrition was working quickly. Haig thought that German resistance might break within two weeks. The inaccuracy of the intelligence being provided was not known and the assumptions and conclusions were understandable given the evidence. The success of the attack on 14 July increased British optimism, Haig describing it as 'the best day we have had in this war'. Haig and Rawlinson were encouraged by the capture of two German regimental commanders and their staffs and the Fourth Army wrote that, "…the enemy is in confusion and demoralised". Later information showed that the Germans had been forced into expedients, such as sending forward a recruit depot as reinforcements. During 16 July, the Fourth Army concluded that it was necessary to organise another broad front attack and that the Germans would use the respite to reinforce Delville Wood, Longueval and High Wood. Rawlinson hoped that the German could be provoked into costly counter-attacks and concentrated on preparing a new attack for 18 July, the German positions being subjected to a constant bombardment in the meantime. Attempts to arrange the next attack and co-ordinate with a French attack on the north side of the Somme foundered due to the effect of the massed bombardments on the ground, made worse by rain which turned it into deep mud, paralysing movement; the attack did not take place until the night of and was a costly failure. Three days later, the Fourth Army noted that German morale was improving, due mainly to better supply of the front line and by the end of July, British hopes of immediate success had faded. In 1928, Henry Jones, the official historian of the RAF, wrote that the battle showed that infantry co-operation would be a permanent feature of British air operations. Recognition flares had proved effective, although there had been too few and infantry were reluctant to risk revealing their positions to German artillery observers. Scheduled illumination was a failure and infantry began to wait for a call from the contact aeroplane by signal lamp or by Klaxon. RFC observers reported that direct observation was the most effective method and that flying low enough to be fired on worked best, although this led to many aircraft being damaged and one