Tizard had several doubts – that the stated size bomber force could be achieved (only 7,000 bombers, not the 10,000 expected); that new navigational aids that would get the aircraft to the targets would not be ready before 1943; and that it was unlikely that more than 25% of the bombs were likely to land on target. As such the strategy would not work with the resources available, and that far bigger effort would be required. In reply to Tizard, Cherwell stated the calculations were for the Prime Minister's benefit, not for statistical analysis, and that despite a difference between the numbers and what was really achieved there would be catastrophic effects. In his work "Bomber Command" Max Hastings characterises the debate between the two sides as not being whether bombing could "raze [Germany] to the ground", but whether it was the most effective allocation of resources. Justice Singleton, a High Court judge, was asked by the Cabinet to look into the competing points of view. In his report, delivered on 20 May 1942 he concluded that: In the end, thanks in part to the dehousing paper, it was this view which prevailed, but C. P. Snow (later Lord Snow) wrote that the debate became quite vitriolic with Tizard being called a defeatist. It was while this debate about bombing was raging inside the British military establishment that the area bombing directive of 14 February 1942 was issued and eight days later that Arthur "Bomber" Harris took up the post of Air Officer Commanding (AOC) of Bomber Command. The study of the effects of bombing on Hull and Birmingham was published on 8 April by Professors Bernal and Zuckerman after Cherwell's paper had been presented. Their work, the "Hull and Birmingham Survey" had actually found that although there was anxiety as a result of the raids, there was no mass anti-social behaviour and "no measurable effect on the health of either town".