lost to a British shell. Artillery-observation was hampered by bad weather but the rolling countryside led to constant demands for sorties for counter-battery fire; when the weather grounded the RFC, attacks could fail for lack of observation. Aircrew photographed the attack front, reported on the condition of wire and trenches, assessed the opposition, linked headquarters and front line and then joined in by bombing and strafing from low altitude. Artillery-observation led to the neutralisation of German batteries, destruction of trenches and strong points and exploitation of fleeting opportunities to bombard German troops in the open. British aircraft caused a feeling of defencelessness among German troops and deprived them of the support of , leaving them dependent on wasteful unobserved area artillery-fire, while being vulnerable to British aircrew seeing muzzle-flashes giving away battery positions. Reinforcements of fighters were slow to arrive on the Somme and prevented from challenging Anglo-French aerial dominance. The morale of British troops was correspondingly increased because German artillery could not conduct observed shoots against them and that German troops could not move without being seen by the RFC. In 1938, Wilfrid Miles, the official historian, wrote that it had been a mistake for the attacking divisions to be held back from exploiting the victory straight away. There appeared to be no Germans left to oppose the 7th and 3rd divisions by when several officers walked forward unopposed. Watts wanted to send the fresh 91st Brigade into High Wood but had orders to wait for the cavalry; Haldane was prevented by the Fourth army HQ from using the 76th Brigade for a pursuit, having to keep it ready for German counter-attacks. Miles wrote that authority could have been delegated to the divisional commanders on the spot, since the 33rd Division had already arrived at Montauban and a vigorous pursuit would have made the prospects for the cavalry much more favourable, when they managed to reach the front line. It may even have been possible for the infantry to penetrate High Wood and dig in on the ridge, threatening Delville Wood and Pozières, rather than the two-month slog that followed. In a 2001 PhD thesis, Kathryn Snowden wrote that the 21st Division succeeded because of the weight and accuracy of the British bombardment enabled the night assembly to take place in safety. The German wire and trenches were destroyed and the few German survivors were relatively easily overcome. Despite