Unknown knife - maybe improvised?

[Jesse Carson]

This is a knife my great grandfather had in WW2 while he fought in the Philippines. As you can see it looks similar to the M3 but the blade is too long and some of the characteristics of the handle are off. I can't find a name for this knife anywhere and was thinking that it may have been an improvised weapon (there are also no markings of any kind anywhere on it). I would greatly appreciate any information anyone has about it.