Gannack's Charge was the name given to an infamous military error occurring on 438.926.M41 during the Spiron campaign. A Sentinel Troop led by Captain Gannack from the 3rd Kalaman Hussars, charged an Ork redoubt containing an artillery battery after confusing their orders. There were no survivors.
The Charge is probably based on the real-world Charge of the Light Brigade during the Crimean War, in which an English brigade misunderstood its orders and charged a Russian redoubt containing an artillery battery. Like the fictional Gannack's Sentinel Troop, the Brigade was completely slaughtered.