Continued Gotha raids in December 1917 had spooked public opinion and, as a consequence, the War Cabinet. The War Cabinet therefore commissioned Viscount French, Commander-in-Chief, Home Forces to report on the state of air defences in London. Today he delivered his report.
In examining the Zeppelin attacks, he concluded that:
“The Zeppelin menace cannot be said to have disappeared. Great improvements have been made in the speed, radius of action, and climbing power of the latest type of Zeppelins, while their visibility has been reduced by camouflaging the underparts of the envelope with black dope. The return of warm weather will probably be the signal for renewed Zeppelin raids, but in view of the recent increases in the defences of London and the south-east of England it is probable that they will direct their attacks on the north-east coast or Midlands. “
On countering the daylight aeroplane raids, he indicated that the reorganization of the gun and aeroplane defences, together with the re-equipment of the defence squadrons with better fighting aircraft, had forced the enemy to give up daylight raids in favour of night attacks.
This, however, created different problems of defence. New improved fighting aeroplanes had been produced and fifty had been delivered to the eight squadrons in the south-east of England. However, only expert pilots could fly these unstable single-seater fighters in the dark and it would take time for the new pilots to become proficient in night-fighting.
The need to provide antiaircraft gun protection for widely dispersed vulnerable points in London and the south-eastern areas made it difficult to arrange an adequate zone for the operation of the large number of Royal Flying Corps squadrons placed between London and the East Coast. The anti-aircraft scheme of fire was based chiefly on sound and it was, of course, impossible, when firing at sound, to distinguish friend from foe.
French noted that, to increase the areas reserved for aeroplane operations, modifications in the disposition of the fixed guns would be necessary. At this point, however it was difficult to determine the ultimate relative value of guns and aeroplanes as weapons of defence, and consequently whether such modifications will even be justified.
French then highlighted the importance of the searchlight. The small 60-m. searchlights supplied for home defence had been effective against the old-type airships, but had proved to be useless against the latest type Zeppelins and against the high-flying aeroplanes. A few 150cm. lights had been obtained from a French firm, and it was expected that deliveries of a considerable number of British-made 120cm. searchlights would begin in the near future. A new type of carbon which would greatly increase the range of the lights was also being manufactured, and sound locators which would enable the lights to be trained on an audible, but invisible, target were being distributed, as were parachute flares to be fired from the anti-aircraft guns. These improvements, he said, “will, it is hoped, have the effect of turning the scale in favour of the illumination of the target. It remains to be seen whether the guns or the aeroplanes will derive the greatest advantage.”
Of the balloon aprons there are three in operation and it is hoped to complete the remainder, up to the authorized total of twenty, at the rate of four each month. The aprons could ascend to a height of 8,000 feet, but the provision of larger-type Caquot balloons would enable them to be raised to 10,000 feet. Their main effect was a moral one, but they tended to keep enemy pilots at heights which made it impossible for them to drop bombs with accuracy of aim.
In addition to these various measures, three hundred Lewis guns had been installed at vulnerable points to keep enemy aircraft from descending below heights at which anti-aircraft gun-fire ceased to be effective, and arrangements had been made to equip with high-angle mountings the machine-guns with the Home Defence Garrison and with Field Army troops.
Finally, to help to establish the height and movements of enemy aircraft, wireless-fitted aeroplanes patrolled given areas: the observers signalled their information to receiving stations which were in direct telephonic communication with the area head-quarters.