Mackensen's overwhelming success in driving the Russians out of Galicia had been mainly due to his artillery, that arm of the military service in which the Germans excelled all their enemies. And here, too, the artillery was to play an important part, for fully 2,000 cannon, nearly all of mid-caliber and heavy caliber, had been brought down against the Serbians. During the first three invasions the Austrians had thrown their infantry up against the Serbian lines. Now German tactics were to be tried: the Serbian trenches and other defensive positions were to be pulverized with powerful explosives, then rushed with infantry.
Though they had been undisturbed for so long, the Serbians were by no means in doubt as to what was yet to come. They had realized that eventually the enemy would return more determined and more powerful than ever. Therefore, they had spent the nine months since the last defeat of the Austrians in extensive preparations. Line after line of trenches had been built back into the interior of the country, and all the possible crossings on the rivers had been heavily fortified. Moreover, they had drained the civilian population of every male person strong enough to carry a gun.
At this time, when the fourth invasion began threatening, their army mustered fully 310,000 men, slightly more than the Austro-German. In regard to small arms and ammunition they were also at least equal to the enemy, for vast consignments of military stores had been sent into the country by the Allies. Only in heavy artillery were they inferior, but then this was also true of all the armies facing the Germans throughout Europe.
Therefore, had the Serbians been called upon to defend themselves only against General von Mackensen's armies, it is highly probable that they would have been able to give the same answer as they had the year previous. So probable, in fact, that Mackensen would hardly dared to have attacked them with only 300,000 men. To be sure, their enemy was no longer made up of raw recruits and there was now the heavy artillery as well as a commander of great ability to face, but the preparations they had made in defensive works, as well as the mountainous nature of their country, more than made up for these advantages possessed by their opponents. It was the Bulgarians who would turn the scale.