Precursors
The 'number of weapons' joke echoes a similar joke in the first episode "The Man and The Hour" of the BBC sitcom Dad's Army, broadcast in July 1968. Captain Mainwaring says "We have one invaluable weapon in our armoury: ingenuity and improvisation", to which Private Frazer replies "That's two."
The trope also occurs in 1964 in Bob Dylan's "Motorpsycho Nitemare," in the form, "Just one condition/You can go to sleep right now/That you don't touch my daughter/And in the morning milk the cow."
Read more about this topic: The Spanish Inquisition (Monty Python)