TFTD is set on near-future earth, and centers on a cross-national force with no particular naming patter. You don't need to know the cannon to help out.

US attack submarines come in three classes - the old workhorse Los Angeles class, the aborted Seawolf class, and the new Virginia class. The LA boats are named after cities (there's a lot of them, list here), the three commissioned Seawolves have no naming system (Seawolf, Connecticut, and Jimmy Carter), and the Virginias are named after states (list here), so depending on what you want, any name not on the above lists would work.

From a broader historical perspective, most attack subs before the LA class were named after fish, a tradition that stretches back to before world war two. When the LAs were comissioned, submarine tactics had changed to the point where they were considered important combat ships, and thus given names of cities (equivalent to traditional cruiser names), and now, they've taken over the traditionally battleship-only state names. So, depending on how old you want your boat to be, you could call her Seattle, Salem, Worcester, or Cleveland for an LA boat, Washington, Delaware, Oregon, or Arizona for a Virginia. Just note that with the Virginias, the Ohio-class ballistic missile subs were also named for states, so you'll want to check against the list. (Older ballistic missile subs were named for historical figures, so no need to worry about them.) For an older boat, it quickly gets hard to pick an unused name - there were a lot of WW2 subs.