The Rapscallion army was led by Gormad Tunn and later on by his son Damug Warfang. The army was very versatile - they sailed the seas or traveled the land based on the way a certain sword landed when tossed in the air. The Firstblade, always a Greatrat, was the leader of the horde. Rapmarks were captains, leading 100 vermin each. Rapscours were scouting officers with twoscore Rapscallions under their command.
Rapscallions were known to be some of the most competent villain grunts in the series - unlike other books, where dozens of vermin are easily slain by one or two goodbeasts, the Rapscallions gave as good as they got, and would have defeated the defending Redwallers if Lady Cregga Rose Eyes hadn't intervened.
Also, their sheer numbers (one thousand), make the Rapscallions one of the largest vermin horde in the entire series, second only to Ferahgo the Assassin's Corpsemakers, and possibly Ungatt Trunn's Blue Hordes.
The Rapscallions appear in The Long Patrol.