Streltsy

Type Object Region Grand Duchy of Moscow Time c. 1550

The Streltsy (стрельцы) were the standing musketeer corps of the 16th-century Muscovite state, first organized under Ivan IV;…

Timeline

c. 1550–1560Moscow · MoscowIvan IV consolidated scattered firearms shooters into a standing Streltsy corps, arming them with matchlocks, axes, and short spears, garrisoning them by district and paying them salaries, thus creating Russia's first large-scale firearms infantry system.
1565–1570Grand Duchy of Moscow · RussiaDuring the oprichnina period the Streltsy expanded in size; some units were incorporated into the oprichnina army to participate in repression of the nobility, while also guarding Moscow and the palace, becoming a key military pillar of tsarist authority.
1563–1570Livonia · LivoniaDuring the Livonian War large numbers of Streltsy were transferred to the front to besiege and defend fortresses, fighting Swedish, Polish, and Livonian Order forces, thereby field-testing the combat capability of Russian firearms infantry.

Streltsy https://www.britannica.com/topic/streltsy
Armies of Ivan the Terrible: Russian Troops 1505–1700 — Viacheslav Shpakovsky (2006)