Because they were marked with the letter K (for Voronezh Komintern Factory),[4][5] Red Army troops adopted a nickname from Mikhail Isakovsky's popular wartime song, "Katyusha", about a girl longing for her absent beloved, who has gone away on military service.[6] Katyusha is the Russian equivalent of Katie, an endearing diminutive form of the name Katherine. Yekaterina is given the diminutive Katya, which itself is then given the affectionate diminutive Katyusha.[7] Katyusha rocket launcher - Wikipedia