The success of the German withdrawal to the Hindenburg Line has been explained as an Allied failure to anticipate the retirement and in being unable seriously to impede it. Another view is that the Anglo-French were not pursuing a broken enemy but an army making a deliberate withdrawal after months of preparation, which retained considerable powers of manoeuvre and counter-attack. Belated awareness of the significance of the building work along the base of the Noyon Salient, has also been given as a reason for a cautious pursuit deliberately chosen, rather than an inept and failed attempt to intercept the German retirement. In "Cavalry Studies: Strategical and Tactical" (1907) Haig had described the hasty retreat of a beaten enemy and an organised withdrawal by a formidable force, capable of rapidly returning to the attack, to defeat a disorganised pursuit.