I began a similar thread roughly a year ago. The best advice I got was a Serrated Edge Pacific Salt. By nature, the serrations have more surface area and dull less quickly than a plain edge. Likewise the serrated edges of the H1 Steel are work hardened and are slower to dull than most all other serrated edged steels. These two attributes mean the blade would require infrequent sharpening or maybe none at all. Depending on what sharpening education your nephew has, the Serrated H1 may be the best bet, as it may not need sharpening during his entire deployment, and would remain sharp and usable during his time overseas. It is also inexpensive enough he could "abuse" it without remorse. I'd recommend this inexpensive, low-maintenance, rust-proof, incredibly sharp blade.
Please thank him for his service for me.