HEAVY GUNS.--Heavy guns of 6-inch calibre, firing a shell of 100 pounds, are used against targets beyond the range of light and medium guns, and with greater effect. _Heavy Howitzers_, of 8-inch or 9.2-inch calibre, are principally employed against covered batteries and strong defences, or for destroying wire entanglements with instantaneous fuses. SUPER-HEAVY GUNS.--Super-heavy guns of a calibre of 9.2 inches and upwards are usually carried on railway mountings, and while they possess a high muzzle velocity, considerable shell-power, and a high degree of mobility (which enables them to come into action in any part of the battlefield where suitable rails have been laid), their arc of fire is very restricted and their "life" is short. _Super-Heavy Howitzers_, of 12-inch or 18-inch calibre, possess similar advantages and disadvantages to super-heavy guns. Their normal use is the destruction of permanent defences, the breaking down of bridges, etc. The 12-inch weapon is also used on tractor-drawn mountings and is highly effective in counter-battery work. The table on p. 173 is based upon particulars given on p. 26 of "Field Service Regulations," vol. ii. (1921). ROYAL ENGINEERS "All arms are responsible for the construction of their own works of defence. It is the duty of the Royal Engineers to assist them by engineer reconnaissances, plans, advice, technical supervision, provision of materials and the construction of works requiring special technical skill. . . . Although trained as fighting troops, engineers should be regarded as reserves to be used only as a last resource; casualties in their ranks are not easy to replace, and they may become needlessly involved in the fighting and lost for work which may have an important bearing on the operations" ("Field Service Regulations," vol. ii. (1921)). {173} TABLE OF ARTILLERY RANGES Weapon Effective Range (Yds.) _Light Artillery_ H.E. Shell Shrapnel Pack Guns (2.75 in.) 5,800 4,000 Pack Howitzers (3.7 in.) 5,900 Horse Artillery Guns (13 pr.) 8,500 5,000 Field Guns (18 pr.) 9,500 5,500 Field Howitzers (4.5 in.) 7,000 _Medium Artillery_ Medium Guns (60 pr.) 15,500 -- Medium Howitzers (6 in.) 10,000 _Heavy Artillery_ Heavy Guns (6 in.) 19/20,000 Heavy Howitzers (8 in.) 12,300 -- " " (9.2 in) 13,000 _Super-Heavy Artillery_ Super-Heavy Guns (9.2 in.) 24,500 -- " " (12 in.) 28,200 -- " " (14 in.) 35,600 -- Super-Heavy Howitzers (12 in.) 14,300 " " (18 in) 23,000 Weapon Maximum Range (Yds.)