@Veshv
The reason the shot had to be the 'center' of the ship was because of three reasons:
1) Lacy only hit 1 shot of his volley.
2) He spaced his volley shots so that there was a 1 cell gap between them.
3) The area where the ship could be was limited
If he had hit 2 shots, that would mean he hit both edges of the cruiser. Otherwise, due to how he spaced his shots + the limited area of the possible placements, 1 shot always means he hit the center of the ship.
@goodknife
That's an interesting point. Definitely based on that search path, the bottom right seemed like a good idea. I wonder if that means he didn't have enough time to search for everything since Oofuna was going to lose soon, and decided to go with the 4 volleys strategy, and that's why he didn't just outright tell Oofuna where the second submarine is.