Need help piecing my Grandpa's WWII story - 39th Combat Engr

[Weston497]

My grandpa's separation papers indicate he was discharged from the 643rd Combat Engineers, who were originally the 39th Regiment Combat Engineers 2nd Battalion.

The papers say he has campaign credit for 

• Sicilian 
  
• Rome-Arno 
  
• Naples-Foggia
  
• Northern Appennines 
  
• Po Valley 
  
• GO 33 WD 45
  

My grandpa shared stories about him being in Salerno and Anzio (not much more than he was there).  Is Anzio part of the Rome-Arno campaign and Salerno the Naples-Foggia?  Also what is GO 33 WD 45?  He also had a Bronze Service Arrowhead and good conduct medal. Are those medals for being in the war, or are they for specific actions?  I feel like someone else has asked this question, but I can't find the thread.  Can anyone point me in the right direction?

As always, thank.