From Lexicanum

The Gudrunite 50th Rifles are a regiment founded around 240.M41 on the planet of Gudrun. Soon after their foundation, the regiment was plunged into battle around the sector. Some of the original foundees were rescued by Ordo Xenos forces led by Inquisitor Gregor Eisenhorn on the Saruthi tetrascape. Later, a squad of veterans accompanied the inquisitor to destroy the Necroteuch

Regimental History

• 241.M41 - The Gudrunite 50th Rifles were newly founded by Imperial standards when they were granted the honour of forming the lead element alongside Tanks of the Thracian Fifth during the infamous 'Triumph of Lord Helican' on Thracian Primaris.

Sources

Eisenhorn Trilogy