That is the story my friend told me...a VMI graduate of Military History who had old B/W pictures of his father in WWII Marine uniform with palm trees and sand in the background...also had a Remington Rand pistol he said his father carried...but was not issued. He said a lot of Marines modified knives, bayonets and trench shovels as field expedient tools.Shooter13 , are you sure it was modified ???
First glance it is a dead ringer for the survival / pilots style knife. Shorter blade , more upswept tip , saw back, 6 flat sides on the bolster ..... when compared to the Fighting knife in the OP.
Only reason I ask is when Camillus Cutlery was going out of business I bought one pilot knife made by them for a retail store ( Brigade Quartermaster ) and one that was to be issued but wasn't , off e-bay.
A subtle difference between the two , but look darn close to yours.