In 2001, Peter Liddle wrote that beyond imposing a delay, the German policy of unyielding defence and counter-attack failed and ought to be judged on the same terms as British and French methods. Haig and Joffre were right to believe that a serious German collapse was possible until late July and a convincing alternative to attrition in the circumstances of late July – early September 1916, has not been proposed. In 2009, William Philpott criticised the weeks of costly, small, narrow-front attacks against a skilful and determined defence by the Germans, yet Gallwitz "had no better tactical method", which reduced operations to a battle of wills. In the Fourth Army area from counter-attacks were made against attacks, exposing German infantry to similar costly and frustrating failures. German artillery and air inferiority was a great disadvantage and led to constant losses. In 2011, Gary Sheffield wrote that analysis of captured documents and prisoner interrogations indicated the strain being imposed on the German army.