Pyotr Semyonovich Vannovsky (Russian: Пётр Семёнович Ванно́вский; Belarusian: Пётр Сямёнавіч Ванновскі, romanized: Pyotr Syamyonavich Vannovski; 6 December [O.S. 24 November] 1822 – 1 March [O.S. 17 February] 1904) was a Russian statesman and military leader of Belarusian extraction, who served in the Imperial Russian Army. He was also an honorary member of the Academy of Military Medical, the Mikhailovsky Artillery School, the Mykolaiv Engineering School, the Imperial Academy of Sciences, and a full knight of the Order of St. Vladimir.

Born in Kiev into a family of Belarusian landed gentry, Vannovsky chose his career early on in his life and began military schooling. After a few years, he participated in the Hungarian Revolution of 1848 and the Crimean War as part of the Life Guards Finnish Regiment, distinguishing himself at the Siege of Silistra, he was highly decorated after the war, becoming the head of his own regiment, and several military schools. During the Russo-Turkish War of 1877–1878, he took the prominent role as the chief of staff of the Ruschuk Detachment, under the Tsesarevich, future emperor Alexander III. Taking part in many minor but important campaigns, especially a campaign for breaking the Siege of Plevna and the battle between Trastenik and Mechka. For his and Alexander's achievements, they were both awarded the Order of St. George of the 3rd and 2nd degree respectively. A few years after the war, Alexander ascended to the throne, and Vannnovsky was subsequently appointed Minister of War.

Vannovsky was one of the most successful Minister of War during the course of the Russian Empire, he was in office during most of the reign of Emperor Alexander III and the early reign of Emperor Nicholas II from 1881 to 1898, he was credited with maintaining order, preventing corruption and reforming the Russian military during his role as the Minister of War. But after Vannovsky resigned, he had warned the military about modern war tactics, should the general's warning be remembered by the generals of the next generation (those who served in the Russo-Japanese War and the First World War), the Russian performance in the Russo-Japanese War and the First World War would have been completely different. He also briefly served as the Minister of National Education from 1901 to 1902. After which he retired and died suddenly in 1904 following the Russo-Japanese War, perhaps dying upon learning of the disastrous war with Japan.

Pyotr Semyonovich Vannovsky was born 6 December [O.S. 24 November] 1822 in Kiev to Semyon Ivanovich Vannovsky, who was from the Gentry Vannovsky family of Belarusian origin from Minsk. His father Semyon was a well-educated man who taught French in the 1st Kiev Gymnasium. And Pyotr, followed to the Vannovsky Family tradition to choose his future career at a young age, he chose to serve in the military and was strongly supported by his father. So as a result, he moved to Moscow and attended the 1st Moscow Cadet Corps, one of the best cadet corps in Russia. Upon graduating, he joined the Life Guards Finnish Regiment, and participated in the Hungarian Revolution against the Hungarian Revolutionaries and the Crimean War as part of the three Finnish battalion Vannovsky's regiment belonged to. In mid 1854, he and the battalions met the Ottomans near the Ottoman villages of Tutrakan and Silistra, and the Siege of Silistra took place. He distinguished himself as a brave but sane soldier during the siege. Later for military distinction, he was awarded the Order of St. Vladimir of the 4th degree with swords and a bow, and was subsequently appointed the commander of his own regiment. After hostility ended in 1857, he became the head of several military schools, and thanks to his efforts, many infantry officers had been trained to take up the post of small unit commander and managing weapons, and those who graduated in the first category was granted the next rank ahead of the schedule. He was later promoted to major-general in 1861.

In 1868, he was promoted to lieutenant-general and was appointed commander of the 12th Infantry Division, this division consisted of the 46th Infantry Regiment of the Dnieper, the 47th infantry Ukraine regiment, 48th infantry Odessa Emperor Alexander I regiment. General Vannovsky, was an overly uncautious man, but unlike the next generation of his (those who served in WW1), he was a well disciplined commander. Constantly going through the life of his men in the army, and carefully engaging in the training of soldiers, making it one of the best division in the Imperial Russian Army. Later he was then appointed chief of staff of the 12th Army Corps in 1871, in which he eventually commanded in the Russo-Turkish War in 1877.

In 1876, General Vannovsky was appointed chief of staff of the newly formed 33rd Infantry Division, which included the 129th Infantry Regiment of Bessarabia, the 130th Infantry Regiment of Kherson, the 131st Infantry Regiment of Tiraspol and the 132nd Infantry Regiment of Bendery. It was a pretty challenging task to form a new unit, but with a determined general such as Vannovsky, he coped with the task easily, which he was noted by the high command of the Kiev Military District.

At the beginning of the Russo-Turkish War, he commanded the 12th Army Corps to crossed the Danube, the Army Corps was later incorporated into the Ruschuk Detachment (the Eastern Detachment), for which he was appointed chief of staff of it, commanded by the tsesarevich, the future emperor Alexander III, whom he would become close friend with after the war. The Ruschuk Detachment was exceptionally powerful among other Russian units. It was composed of the 12th and the 13th Army Corps, 49 battalions, 19 Cossack divisions and 224 guns. The task of the detachment was to take the small Ottoman towns of Ruse and Nikopol, but when they arrived, they were attacked by the Ottomans and as a result, they went fully defensive, but they could still break through the Ottomans and won significant victories. Later on the Ottomans launched at Katselovo, forcing the Russians to retreat to Gorsko Ablanovo. There, another battle would take place, which would once again end in an Ottoman victory. After some time, the Ottoman high command made a decision to attack the right flank and the center of the Ruschuk Detachment with 28 squadrons and 84 guns, in order to encircle the detachment from the rear. But the plan was later unravelled by Vannovsky, and the Russian Army soon went to defensive position. On 9 September, when the Ottomans attacked, they got counter-attacked by the Russians, inflicting considerable casualties on the Ottomans; nevertheless, the Ottomans had emerged victorious.

Now with Plevna captured, Commander-in-chief Grand Duke Nicholas Nikolaevich changed the original plan completely, the Ruschuk Detachment went completely defensive, with the task of continue protecting the Russian rear.