You need 64 bit integers for holding indexes into arrays with more than 2 billion elements.

Unsigned ints will double that.

Actually, you pretty-much HAVE to have a tracking sensor on the missile itself if you want to hit anything.

However, if you fire off a missile in a random direction you're going to blow up some ship at random at best - most likely a tanker. Also, radar is subject to jamming, and you bet that if somebody spots a radar emitter travelling at mach 3 they're going to jam it! IR or visual is only useful if you have a very good idea of where the target is - it can't search a large area. Even radar on a missile will only spot something in a cone maybe a few miles across, which isn't much even in the Persian Gulf.

Keep in mind that a cruise missile is exactly the kind of threat that US naval defenses were designed to counter. The only twist here is sneaking one onto a merchant ship.