Next to mining, the most nerve-racking form of trench warfare was provided by the trench-mortar. Towards the latter end of August the enemy began to make a considerable use of these weapons. In consequence the trenches were frequently severely damaged, and many casualties were sustained. The British trench-mortars were in these days only in their early experimental stages; moreover, difficulty always existed in obtaining sufficient ammunition for them to be of any real service.
The enemy, on the other hand, appears to have had an unlimited supply of ammunition for mortars of a considerably heavier calibre and longer range than ours. At this time his commonest types were those that discharged the "oil can" or "rum jar" and the aerial torpedo. The "oil can" was little more than a tin canister about nine inches in diameter, filled with high explosive, and fitted with a time fuze. In those days it was fired from a smooth-bored wooden mortar, and in consequence turned over and over in its flight, and was therefore not particularly accurate. The explosion was, however, terrific, devastating to wire or trenches, and most trying to the nerves of any one who had to live in an area in which they habitually burst.
The aerial torpedoes had a fixed propeller which kept them from turning over in the air, and were in consequence a more accurate projectile. Their effects were if anything worse than those of the "oil can."
The Division had attached to it one 1-1/2-inch mortar battery and a 4-inch mortar battery for which ammunition was available only in small quantities. On 2nd September, a 2-inch trench-mortar battery arrived, though its ammunition did not join it till 7th October.
The 2-inch trench-mortar fired a bomb exactly similar in shape to the hammer used in Highland games in "throwing the hammer." For this reason it was known to the troops as "Donald Dinnie." It was also known as the "Plum Pudding" or "Football." It was on this account that an English brigade-major was once heard to confess that he had always thought "Donald Dinnie" was Scots for plum pudding.
The "Donald Dinnie" was an excellent projectile when it burst in the right place. Sometimes, however, it did not burst at all, while at others it burst within a few feet of the mortar. Again, the mortar frequently misfired. Trench-mortaring was rather a game of chance in those days, with the odds slightly against the man firing the mortar.