Capable of delivering over 3000hp the Big Lizzys were a formidable match for Gresley's A4. The first 10 locos of the class were built with a streamlined cladding colloquially referred to as an upside down bathtub. Due to the added weight and maintenance difficulties, the streamlining proved nonviable and it was later removed revealing a locomotive of very handsome lines. The remaining 28 locos were built without streamlining and the class became commonly known as Duchesses.