Oliver,
There is a more detailed and more reliable biography of Hermann (in Russian):
Below is my short compilation of his biographies:
Hermann was born in Saxony, entered the Russian service in 1770 as a “podporutchik” (sub-lieutenant), at first served as a quartermaster officer. He took part in the Russo-Turkish war (1768-1774), was present in the battles on the rivers Larga and Kagul. In 1770, Hermann was ordered to carry out a military survey and to draw maps of Moldavia and Valahia. After he had finished this work in 1772, he was appointed senior quartermaster to the Corps of General Elmpt in Poland.
Then Hermann was appointed to the Observation Corps on Swedish border, and drew a map of Finland.
In 1773, Hermann was appointed senior quartermaster to General en Chef Bibikov in Orenburg region. Hermann took part and in the suppression of Pugatchev’s rebellion (1773-1775). In 1774, being in command of the advance-guard of a detachment under the command of Prince P. M. Golitsyn, Hermann fought in several combats, and on 7 May 1774 he was promoted major.
In 1775 and 1776, Hermann carried out surveys and drew maps of several border regions of Russia.
In 1777, Hermann was promoted lieutenant-colonel and transferred to the Kabardinsky Infantry Regiment. He constructed a line of forts and small fortresses in North Caucasus region.
In 1778, Hermann designed the new fortress of Kherson, and was ordered to construct it.
On 1 January 1782, Hermann was promoted colonel. In 1783 he was appointed commander of the Vladimirsky Infantry Regiment. He took part in various expeditions, including General Tekeli’s expedition to Anapa, constructed two small fortresses on the River Kuban, and drew a map of Caucasus region.
On 21 April 1789, Hermann was promoted brigadier. On 5 February 1790, he was promoted major-general and appointed commander of an infantry brigade (Kabardinsky, Vladimirsky, and Kazansky infantry regiments). When the Turks under the command of Batal-pasha invaded the region in 1790, Hermann did not wait for other Russian detachments, which marched to join him, but marched forward to meet Batal-pasha and defeated him on the River Albazinka on 30 September 1790, captured the camp of the Turks and all their artillery (30 pieces). On 21 January 1791, Hermann was awarded with the order of St.George 2nd class and with land estates in Polotsk region with 500 “souls” (adult male peasants) for this victory.
In 1792, Hermann was appointed general-quartermaster of the army under the command of General en Chef Krechetnikov in Lithuania.
In 1793, Hermann was the commander of the right wing of the army, distinguished himself in several combats, and was awarded with the order of St.Anna.
In 1794, he served under Prince Repnin, and took part in the assault on Vilna. He was awarded with the order of St.Vladimir 2nd class for this campaign. In 1795, he was a general-quartermaster under Prince Repnin.
On 27 December 1797, Hermann was promoted lieutenant-general. In 1798, Hermann was appointed general-quartermaster of the whole Russian army and awarded with the order of St. Alexander Nevsky. In 1799 Hermann was appointed to command a part of the Russian troops, which had to be sent to Italy, but then he was replaced with Alexander Suvorov, with Hermann as an advisor. Later Hermann was appointed to command the Russian troops, which were sent to join the British troops under the command of the Duke of York. At the battle of Bergen, at first Hermann’s troops fought successfully, they captured 14 artillery pieces and about thousand prisoners, entered the town of Bergen, but there they got in disorder and were defeated. Hermann was taken prisoner.
Before the information on the battle of Bergen had reached St.Petersburg, Hermann was promoted general of infantry (24 September 1799). The French sent Hermann to Lille. Tsar Paul expelled Hermann from the army. Hermann returned to Russia only after the peace was concluded between France and Russia. On 6 November 1800, Hermann was restored in the army, but got no appointment. He died on 9 June 1801.