01. Move: set up your next decision.
Move takes you one cell north, south, east, or west. Diagonal moves are not allowed, and you cannot enter islands or leave the map. Use it to approach an opponent, clear an island blocking your line of fire, or leave a location where you made a sound.
Your opponent is not told that you moved; they only see that your turn has passed. You can even move into the cell your opponent occupies. Nothing happens when that occurs: there is no collision, no notification, and no detection. Each cell represents an area of sea rather than an exact point, so moving never works as a free way to find the enemy.
Before moving, consider what you want to do next turn. If you want to fire a torpedo, you might try to line up with a row or column containing a possible enemy position. Remember that your opponent can move too; a possible position is not a certainty.
02. Wait: staying put is a choice.
Wait ends your turn without changing your position. Like a move, it is not reported to your opponent, so they cannot tell whether you moved or stayed. It can be useful when you want to hold your location and see what happens. Waiting alone does not provide a new sonar reading, though. Remaining in place is risky if your opponent has probably worked out where you are.
03. Sonar: gain a clue, give one away.
Sonar scans a square that extends up to 4 cells in every direction from your submarine (a 9 × 9 area, trimmed at the map edge). Islands do not block it. If the enemy is inside, you learn their sector, their direction, and a distance band. The direction is one of eight compass points and covers a whole quadrant: “northeast” means anywhere up and to the right, not exactly 45 degrees. The distance band is 0 (same cell), 1, or 2–4.
If the enemy is within 2 cells, you also learn which 2 × 2 block of cells they are in. Sonar never returns exact coordinates. “Not detected” means the enemy was not inside that square at the time of the scan, not that there is no opponent. There is no limit on how often you can use sonar.
The cost is that your opponent always learns which sector you transmitted from, whether or not you found them. If you did detect them, they are also told they were detected. If they are within 2 cells of you, they learn the 2 × 2 block you are in. Before scanning again, check whether the previous result already narrows the possibilities enough.
04. Torpedo: check direction, range, and ammunition.
A torpedo travels in a straight line north, south, east, or west for up to 4 cells. It hits the enemy if they are in any sea cell it passes through before its range runs out or it reaches an island; an island stops it, and it cannot pass through. Your own cell is not part of its path, so while both submarines share the same cell, a torpedo cannot hit. A diagonal sonar reading does not let you fire a diagonal torpedo.
You have 12 torpedoes per match. Only you can see how many remain. If your last torpedo misses, you lose immediately; if it hits, you win. Firing reveals your sector to your opponent, and if they are within 2 cells of you, the 2 × 2 block you are in. Your exact cell, the direction of fire, and where the torpedo stopped are never revealed. If you miss, consider whether you should stay in the position you fired from.
05. Turn timer, turn limit, and disconnections
You have 45 seconds to act on each turn. If time runs out, the server takes a Wait on your behalf: you keep your position and the turn passes to your opponent. The countdown on your screen is for display only; the server keeps the official time.
A match lasts at most 100 turns. The two players alternate, so each gets 50 actions. If nobody has hit or run out of torpedoes by then, the match is a draw. You can also forfeit at any time, which counts as an immediate loss.
In matches between people, a player who has not been in contact for 15 seconds is treated as disconnected. They then have 60 seconds to return to the same match, and the turn timer is paused while they are away, up to 120 seconds in total per match. If they do not return in time, they lose. In CPU matches, a brief connection drop does not count as a loss.
Three questions after your first match
- How many turns old was the sonar reading?
- Was an island blocking the direction you fired in, or was the target beyond 4 cells?
- Did you move after the last time you made a sound?
Looking at these questions, rather than only the result, helps you understand your decisions. No fixed sequence guarantees a win. Updating your hypothesis as your opponent acts is part of the appeal.