Billy vs Chip

Billy

name

  • A diminutive of the male given name William. 

  • The B-25 twin-engine bomber aircraft used during World War Two, commonly called the "B-25 Mitchell" in honor of U.S. Army General William "Billy" Mitchell. 

Chip

name

  • A diminutive of the male given names Christopher and Charles. 

How often have the words Billy and Chip occurred in a corpus of books? (source: Google Ngram Viewer )