This military unit was one of the first-priority regiments in the Don Host. It was also one of the finest and most combat-effective units. The numbering of regiments was introduced by the Don Host during the Russo-Turkish War of 1828–1829. Before that, regiments were known after the names of their commanders. However, even after the introduction of numbering, the regiment’s composition was changing constantly for a long time. It meant that a regiment could be formed in one of the four military districts of the Host, assigned a number, and sent to Georgia, Poland, Bessarabia, or other regions for three or four years. After that time, the regiment returned to Don where it was dismissed, and its number was assigned to any other newly formed unit.

 
In the 1870s, regiments were grouped according to their priority, and the first twenty regiments manned with young twenty-year-old Cossacks, the so-called first-priority forces, received permanent numbers and home stations. Every year after that, a new shift of one hundred and fifty or two hundred Cossacks from certain stanitsas went into military service with the same regiment. Having completed four years of service, the Cossacks returned to their stanitsas.

 
In the event of war, older Cossacks were drafted according to clearly defined rules. Those under 30 were conscripted into second-priority regiments and those between 30 and 35 years old — into third-priority regiments.

 
In the early 20th century, regiment No. 12 was formed of the young Cossacks from the stanitsas Kazanskaya, Migulinskaya, and Vyoshenskaya. Sometimes Cossacks of the Yelanskaya stanitsa also joined the regiment. Before World War I, the 12th Don Cossack Regiment was part of the 11th cavalry division and was stationed at a little place called Radzivillovo in the Volhynian Governorate. Grigory Melekhov, the main character of Mikhail Sholokhov’s novel “And Quiet Flows the Don”, and several other literary characters served in the 12th Don Cossack Regiment.