In 1756 the Seven Years' War was threatened. A league was formed by the Court of Vienna for stripping the King of Prussia of his dominions. The French threatened the electorate of Hanover, and formed an alliance with Sweden and Austria against Britain and Prussia, the king of which, on receiving evasive answers from Vienna as to the object of the Austrian armaments, prepared for immediate strife.
Anxious for employment, and remembering, perhaps, the manner in which Frederick II. had insulted him at his levée in Berlin, the enterprising spirit of Loudon induced him to visit Vienna and solicit a command against Prussia; but having left his regiment without obtaining leave of absence, he was on the point of being reprimanded and ordered back to Croatia, when by good fortune he obtained the friendship and patronage of Prince Kaunitz, the head of a noble family, whose possessions lie on the Iglau in Moravia. By the prince's interest he was appointed Lieutenant-Colonel of eight hundred Croats. These wild and hardy troops were destined to be ordered on every desperate service, and as their mode of fighting resembled in every respect that of the Pandours, Loudon was well fitted to command them; more especially as he had acquired their dialect while quartered in their native province. They were all clad in short waistcoats with sleeves, long white breeches, light boots, and rough huzzar caps. They had each a long firelock with a rifle barrel and short bayonet, a crooked sabre, and brace of pistols. This corps formed part of five thousand Croats levied by the Empress-Queen for the new war against Prussia. Like the Pandours of Baron Trenck, they had no pay or provisions, but such as their swords and the terror of their presence won them; and as irregular troops they were a scourge wherever they marched.
On the 29th of August, 1756, the King of Prussia entered Saxony at the head of seventy battalions of foot and eighty squadrons of horse, in three columns, which marched by three different routes, but formed a junction at Dresden and captured it. The Elector, who was King of Poland by the title of Augustus III., took refuge in a camp at Pirna, while Frederick marched into Bohemia and found the Austrians encamped at Lowositz under Marshal Count Brown, who was defeated there in October; and after a long and bloody contest forced to retire in rear of Egra.
It was at this time that Loudon with his Croats joined the Austrian army; and in the disastrous retreat which ensued after Lowositz, he narrowly escaped when a hundred of his grenadiers were slain by the Prussian hussars. During Marshal Brown's retreat out of Saxony, Loudon took by surprise the town of Estchen at the head of five hundred men, and destroyed two squadrons of Prussian hussars. This was his first exploit, and it was deemed the most brilliant of the Austrian campaign.
He distinguished himself again at Hirschfeld, on the Bohemian frontier; and for his bravery on that occasion was appointed colonel in February, 1757.
On the 20th of that month his corps had formed part of the six thousand Austrians who attacked the Prussian position at four in the morning. Loudon fought with incredible bravery, and slew many of the enemy with his own hand. In August he attacked the Schriekstein and captured three hundred newly raised soldiers. He now obtained an increased command—a small division, six thousand strong, consisting of Croats and Pandours. With these he attacked and defeated a body of the enemy at Erfurth, a garrison town of Saxony. He then joined the now allied French and Imperialists, who marched to Weissenfels, a city in the centre of Thuringia. By this time the Swedes were pushing on the war in Pomerania and had besieged Stettin. Marshal Richelieu with eighty battalions and one hundred squadrons of French had entered Halberstadt, and was everywhere levying contributions with fire and sword, while the Austrians had made themselves masters of Lignitz and most of Silesia; and after laying siege to Schwiednitz, were preparing to pass the Oder. Everywhere the tide of war had turned upon the King of Prussia.
Loudon was now with what was named the Combined Army. The Prince de Soubise commanded the French; the Prince of Hildburghausen led the Austrians, and their united and immediate object was to clear Saxony of the Prussians. Frederick left a division to cover Silesia, and approached this Combined Army, which passed the Sala and established its head-quarters at Weissenfels; from whence the Comte de Mailly was sent to summon Leipzig. On the 5th November, the King of Prussia gave battle to this Combined Army, then fifty thousand strong, at Rosbach, a village of Prussian Saxony, at eleven o'clock in the morning. The allies were formed in line with their cavalry in front. The impetuosity of the Prussian infantry, whose charge was admirably sustained by a fire of artillery and advance of horse, broke the allied line, and, notwithstanding all the efforts of the Prince de Soubise, Frederick obtained a complete victory with the loss of three hundred men only; while the Combined Army lost no less than eleven generals, three hundred other officers, nine thousand killed, wounded, and prisoners, sixty-three guns, twenty-nine colours, and one pair of kettle-drums. With the battle of Rosbach terminated the campaign in Saxony.
Loudon was with the Combined Army during all these operations; and the Prince of Hildburghausen, desirous of signalizing his own authority by some grand stroke, proposed to the Prince de Soubise the project of dislodging the Prussians from the petty principality of Gotha, where Seidlitz commanded. They began their march accordingly with their grenadiers and Austrian heavy cavalry, while Loudon led the Pandours and French light dragoons. They dispatched one column of cavalry over the heights which led to Thuringia; another on the left, preceded by hussars, approached Gotha from the side of Langensaltza; while Loudon with the Pandours, dragoons, and a body of grenadiers, formed the column of the centre.
Seidlitz was ready to receive them. He was in order of battle, and had all the defiles secured by horse and cannon. A desultory conflict ensued among the woods and mountains; and though the Prince de Soubise cut a passage to the castle wall of Gotha, he was obliged to retreat and leave three officers and one hundred and sixty soldiers in the hands of Seidlitz. The Prussian column under the Prince of Bavern attempted to cover Breslau, which surrendered on the 22nd November to the Austrian generals, by whom he was made prisoner; while the remnant of his army joined Frederick, and on the 5th December the battle of Lissa, where he gained a signal victory, was fought in Silesia. Such was the severity of the season that many hundreds of soldiers were found dead on their posts; and the German generals were reproached with heartlessly exposing their men to the extremity of cold; for a campaign in winter is alike opposed to the dictates of humanity and the common rules of war, as the operations of our own troops in the Crimea have given terrible proof.
In these arduous duties, though always at the head of his Croats and Pandours, Loudon never received another wound, though exposed almost daily to balls, bayonets, and sabres; and it is worthy of remark that the musket-shot received at Zabern was the only scar of his long military career.