I'm in the military. Most servicemen and women are not knife enthusiasts, so unless your buddy happens to be the exception, I would bear that in mind when making a selection. With that, I would stick with an entry-level or mid-tier stainless steel for corrosion resistance and ease of sharpening. I would also get him something reliable and durable. Servicemen and women travel to austere locations where environmental conditions can be extreme. If a knife mechanism is so delicate that it requires a teardown simply because it was dropped in the muck, it's not going with me when I deploy. I want a knife that I can clean under a faucet and put back in my pocket. Additionally, if he is new to knives, he is more likely to abuse your gift while learning its limits.
I concur with those who have recommended a folder over a fixed blade. Most fixed blades that deploy with service members never see the light of day. Instead, they sit at the bottom of gear bags "just in case." However, a good folder is likely to see daily use. Multi-tools are a great option too, but I prefer a folder for its ease of access. I always deploy with a multi-tool, but I keep it with my gear for emergency repair work, whereas my folder is on my person every day.
One final word on edge configuration. A lot of servicemen and women love partially serrated edges. That usually stems from a fear of getting trapped in a downed vehicle and needing to self-extract by cutting through a heavy safety harness. I share that concern, but I'm a knife enthusiast, so I keep my blades sharp. But perhaps a partially serrated blade isn't a bad idea for someone who lets his blade go dull. Serrations will usually cut, even when they've been neglected. Meanwhile, others avoid using them so that they are sharp when needed. Something to think about.