In the book called "Battle Stars and Naval Awards" including Presidential Unit Citations and Navy Unit Commendations, I can find no really clear-cut criteria for the awards of battle Stars or the other awards mentioned.
However, there was never more than one battle star awarded for a single engagement or operation.
Exactly how severe a battle or operation had to be to earn a battle star is not made clear. IF anyone knows for sure I would appreciate the answer. The book merely states that ships or units facing the "ordinary hazards of war" would NOT be eligible for a battle star.
My ship came under several air attacks including more than one attack by torpedo planes and we were awarded only ONE battle star.
I believe the Armed Guard AND the Merchant Marines may have been "short-changed" in more ways than one! (And MANY other military units were, also)!
Oh, well...we can't dwell on the past...we should only be thankful we made it back when so very many did not.
The book I mentioned probably is still available at www.BattleStarsAndNavalAwards.com or contact the author at: Tamaroa@aol.com. I paid $29.95 plus $3.00 for my book. It is a great book to broaden our knowledge of different ships and units.
I hope this has been of some help.