Granny (Irene Ryan) trains some of the castle servants in military matters to make them guerrilla fighters. She stated she was hoping to turn them into the Dirty Dozen, a reference to the movie "The Dirty Dozen" (1967), which had been released the year before. It's a rare instance of Granny mentioning a contemporary film, since she's normally stuck in the silent era.
The title is based on the The War of the Roses, a series of fifteenth century civil wars fought in England between supporters of the Houses of Lancaster and York.
Naming the butler Tetley was likely a joke, as it's a popular brand of English tea and the Brits are famed for their love of the beverage.