I was reading all the suggestions people were offering this man to help him select a quality combat kinfe for his son. He was already on the right track himself as far as KABAR and especially Fallkniven were concerned. I agree Bark River was a good suggestion, however as many are carbon blades they rust and require maintenence, a burden for a soldier.
Stay away from cheap offerings like Gerber LMF II. This not a nine lives knife. While it may stand up to one beating, it rarely handles a subsequent one. It is not full tang and is worse than KABAR. My only suggestion is Fallkniven. They are the strongest commercial knifes in the world. My persoanl suggestion is the S1. Why? Its full tang, A1 is not, so S1 is (proportionally) stronger than A1. S1 (190g) is lighter than A1 (305g), the latter of which some have described as like 'carring around a sharpened crowbar.' S1 performs adequetly in survival situations including battoning and light chopping. S1 is 5mm thick, A1 is 6mm thick making it awkward for utility tasks like food preparation. A Royal Marine once described trying to extract a jammed round from a 20cal. as almost impossible using the A1, because it was too thick. Now the S1 has an decent tip for penetration A1 does not, and the A2 is even worse in this department, and or for the former gun jam task forget it as well. A2 is too heavy at almost half a kilo, and Fallkniven does not categorised it as a military knife.
In conclusion A1 has the reach at 6.3" where S1 is 5.1". KABAR has a 7" reach and its blade is thinner than both although I am not a fan of its penetration ability or durability in comparison to the S1 and A1. Don't missunderstand me A1 is a very, very strong knife indeed, more so than KABAR and if you want the longer reach over an S1 choose the A1. If you want somthing shorter, but lighter, faster and pointier- with good penetration thats still way strong choose the S1. He should have a standard issue bayonett to fit his M16 A2 Rifle, so my recommendation would have been the S1 based on its lightweight, strength and winning penetration ability for combat.