In the operations of the new year the King of Prussia recovered Schwiednitz from the Imperialists on the 16th April; entered Moravia on the 27th May; invested Olmutz, which was stoutly defended by the governor, General Marshall, a Scotsman; while Marshal Daun, under whom Loudon held a command, took post on the adjacent mountains, to intercept and cut off the Prussian convoys. The siege had now been open for four weeks, and the trenches were rushed with great vigour by the Scottish exile--the gallant Marshal Keith--notwithstanding the great difficulties attending it; for Loudon, bravely, and at incalculable hazard, in the defiles of Damstadt, in the principality of Lichenstien, intercepted a convoy of four hundred waggons, and obliged General Zeithen, who escorted them with twenty squadrons and three battalions, after a five hours' encounter, to retire on Trappau. This loss was irreparable, for General Putkammer, eight hundred men, and the _military chest_ were taken. The King of Prussia was compelled to raise the siege, and effected one of the most able retreats ever seen in Germany; he then marched to oppose the Russians, who had broken into Brandenburg under Generals Brown and Farmer, two Scotsmen, whom he met in battle at Zorndorf, defeated on the 25th August, and drove them into Poland. Had Loudon (who was ably seconded by Daun) _not_ intercepted General Zeithen, "the town of Olmutz must have been taken in a fortnight," says Frederick, who styles it the Battle of the Convoy; "for the third parallel was finished, and the besiegers had begun to open the saps." For this service Loudon received the rank of lieutenant-field-marshal. He had now won the reputation of being the first cavalry officer in the service of the Empress-Queen; and he was of great use to Daun in galling and incommoding the King of Prussia during the retreat from Olmutz. With four thousand men he took post in the wood of Opotshno, a Bohemian town, fifteen miles north-east of Koningengratz, where he intended to attack the Baron de la Mothe Fouque, who with thirty-two battalions and squadrons was conveying the heavy siege train. But there Loudon was unexpectedly assailed by Frederick, who had heard of his projected ambush, and marched to attack him in it, and he was forced to retire through the forest with the loss of a hundred Croatian troopers. He retreated towards Holitz, and thus the siege train passed unmolested to Glatz.