In 1995, Simpson wrote that the inability of the British artillery adequately to respond to the changes of German tactics may have been caused by the supply difficulties in October, when the gunners lacked the ammunition to extend creeping barrages all the way to the far side of German defences. Guns were worn out, ammunition had three types of propellant with inconsistent characteristics, all the ammunition was damp and corrections for atmospheric conditions were insufficient to regain accuracy, without observation of targets or information on the fall of shot from artillery-observation aircraft. In 2001, Simpson described the process of forming plans by the Fourth Army headquarters to be one of consultation and negotiation with corps commanders, provided that decisions were compatible with the corps artillery plan, which was derived from the army plan. Corps then set boundaries and let divisional commanders have discretion within them. By October corps headquarters were aware of the importance of passing information from contact-patrol aircraft and other sources forward to divisions, the corps headquarters developing into information clearing-houses by the end of the battle.