Roy,
I imagine you might want to wait to see what boat your grandson gets assigned to before buying, BUT, depending on your experience with Submarine models, you may want to try your hand at one now.
Some current Plastic kits covering the latest classes of US Subs in 1/350 scale:
HobbyBoss makes a Virginia Class
Bronco makes a Seawolf Class
Dragon make an Ohio SSBN class and the Florida SSGN
Hobby Boss makes the Los Angeles Class
HobbyBoss also makes a 3-in-1 LA class kit covering SSN-688/VLS/688I versions.
Riich makes an LA class flt I and flt II VLS and flt III Improved
WarshipGuy brought up the Micro-Mir kits. Very nice kits and lots of USN subs to choose from. In fact, Micro-Mir has more classes of US Subs in 1/350 than any other manufacturer. Both Bill and I recommend them. However, there are no alignment pins on their hull halves and this can be a tough situation for a modeler unless you have experience with it. Aligning the hull halves is The Most Important Step, otherwise you will be puttying,sanding, and scraping which can ruin the fun. It's good to have some experience with PE too as many of the kits have brass props and some kits, like the Albacore, have tiny parts like Cleats to be attached to the deck.
Once FreeTimeHobbies re-stocks, I recommend them for Micro-Mir.
Several other online retailers also sell Micro-Mir like HobbyLinkJapan.
My favorite Micro-Mir overseas-retailer is ModelsUA, a Ukraine online shop. Good prices and even better stock than FreeTime.
One important thing... Micro-Mir does not currently have models of US Subs currently in service. Their USN kits cover the Cold War era Submarine classes: Growler, Nautilus, Albacore, Skipjack, Skate, Thresher, Sturgeon (short & long hull like Parche), George Washington, Lafayette, and Benjamin Franklin. They do make several models in each class to cover differences within that class like the USS Daniel Webster, a Lafayette class.)
Be aware that there are some accuracy issues on some of the Micro-Mir kits. For example, no vertical stabilizer on the stern diving planes on their Benj. Franklin class subs. Note that the other manufacturers kits are not always perfect either.
Roy, Good luck to your Grandson. I hope he makes his qualification quickly. Let us know where he gets assigned.
Nino
P.S. If you want a run-down on 1/700 kits or Resin models, just ask.