The character Rip van Winkle sings part of an aria from the famous German opera "Der Freschutz". Another nod to the opera is in her weapon, a musket which can fire "magic bullets" that pierce anything. She also likens herself to Kaspar, the protagonist of the opera.
The Major says in his speech "Finally the sea lion has left the ocean and is heading up the hill!". This is a reference to Operation Sea lion which was the invasion plan of England during WWII.