 British fighter aircraft tried to prevent German aircraft observing for their artillery , by dominating the air from the British front line to the German balloon line , about 10 @,@ 000 yards ( 9 @,@ 100 m ) beyond . Better aircraft like the Bristol Fighter , S.E.5a and the naval Sopwith Triplane had entered service since Arras and matched the performance of the German Albatros D.III and Halberstadt D.II fighters . The " barrage line " was patrolled all day for the week before the attack , by fighters at 15 @,@ 000 feet ( 4 @,@ 600 m ) with more at 12 @,@ 000 feet ( 3 @,@ 700 m ) in the centre of the attack front . No British corps aircraft were shot down by German aircraft until 7 June , when 29 corps aircraft were able to direct artillery fire simultaneously over the three attacking corps . Behind the barrage line lay a second line of defence , which used wireless interception to take bearings on German artillery observation aircraft and guide British aircraft into areas where German flights were most frequent . By June 1917 , each British army had a control post of two aeroplane compass stations and an aeroplane intercepting station , linked by telephone to the army wing headquarters , fighter squadrons , the anti @-@ aircraft commander and the corps heavy artillery headquarters . 
