GUPPY, or Greater Underwater Propulsion Power Program, was a modernization campaign for World War Two built US submarines, in the late 1940s and early 1950s.

GUPPY II was for the Balao class
It included:

• Streamlined sail
  
• 3 new masts
  
• snorkel induction
  
• Snorkel exhaust
  
• ESM mast
  

GUPPY III was also applied to Balao class submarines, many GUPPY II subs were modernized with it.
GUPPY III was much more extensive than GUPPY II, it included:

• It cut in half and lengthened with a 3.8m extension put in forward of the control room for a new sonar room.
  
• Gave subs the ability to fire the mk. 45 nuclear torpedo.
  
• Added BQG-4 sonar
  

Today, only one GUPPY III configured submarine, the USS Clamagore, survives, as a museum at patriots' point with the USS Yorktown (CV-10).