BATTLESHIP
15 Achievements
1,000
8-10h
Radar Specialist
Detect a total of 50 ship's coordinates before hitting them.
100
14.16%
How to unlock the Radar Specialist achievement in BATTLESHIP - Definitive Guide
The second player doesn't need to play at all. They can just press to skip their turns. I do not believe that player 2 can earn any achievements.
You will probably get this as you are going after the other trophies as one of the biggest parts of the game under "clash at the sea!" rules is detecting your opponent's ships using your white attacks. White attacks are ones that locate the enemies ship locations without doing damage to their ships (only the mines & torpedoes do actual damage). When you are playing campaign mode, that's the rules it uses so that is when you will most likely will get it. Just keep using your different white attacks to find the enemies ships without hitting them with a damaging attack (red damaging attacks or the white attack with damage inclusion like torpedoes or mines). Once you find your 50th ship, the trophy will pop.
You can detect a ship's coordinates by using your white resources. They will turn green when you detect an enemy. Then hit them with your red resources. This will likely unlock through normal play as you complete the campaign. If not, you can replay levels to get it.