How to play Sea Battle (Bắn Tàu): hide your fleet, sink theirs

The sea and the fleet, placing ships, firing, hits and sinking, and tips, for 2 players.

Updated 23 October 2026

Sea Battle is the guessing game many people first played on squared paper at school: two players hide a fleet of ships on a grid, then take turns calling out cells to fire at until one fleet is sunk. In Vietnam it is known as bắn tàu trên giấy.

In GatherPlay's Sea Battle each player places their ships on their own phone, and the shared screen shows both seas with every shot, so the whole room can watch. The server keeps the fleets secret and checks every shot, so nobody can peek or fudge a hit.

The goal

Sink all five of the other player's ships before they sink yours.

The sea and the fleet

• Each player has a sea of 10 by 10 cells. Rows are A to J and columns 1 to 10, so every cell has a name like F5.
• The fleet has five ships: the Carrier (5 cells), the Cruiser (4), the Destroyer (3), the Submarine (3) and the Patrol boat (2). That is 17 cells to find.
• Each ship lies in a straight line, across or down. Ships may touch each other but never overlap.

Placing your ships

1. Tap a ship below your sea, then tap a cell: the ship starts there. Near the edge it slides back inside.
2. Tap a placed ship to pick it, then tap it again to turn it, or tap another cell to move it. Remove takes it off.
3. Shuffle places the whole fleet at random if you are in a hurry.
4. Tap Ready when all five ships are placed. You can change your mind until the other player is ready too.
5. When the placing time runs out (90 seconds by default), any ships not placed yet are placed at random.

Firing

1. The game picks who fires first.
2. On your turn, tap a cell of the other sea to aim, then tap Fire. Two taps, so a stray touch never wastes a shot.
3. Every shot is a miss, a hit, or sinks a ship: the hit on a ship's last cell. Everyone sees the result, and which ship sank.
4. By default a hit or a sinking lets you fire again, and a miss passes the turn. The host can switch to the classic rule: one shot per turn.
5. The first player to sink the whole other fleet wins. Then both fleets are shown.

Tips

• Hunt on a checkerboard: every ship covers at least two cells, so firing at every other cell finds them all with half the shots.
• After a hit, try the four cells around it, then keep going along the line until the ship sinks.
• Watch the fleet list. If only the Patrol boat is left, gaps smaller than two cells can't hide anything.
• Spread your ships out, but don't be predictable: ships along the edges are a habit many players have. Ships may touch, and a Patrol boat tucked against the Carrier is easy to miss.

Playing apart

Start a Discord or Google Meet call and share the shared screen's browser tab, or skip it: each phone shows the other sea, a map of your own and every shot, so you can play from anywhere with the code.

Start a game

1. Open GatherPlay on the TV and host a Sea Battle game.
2. The two players join with the QR code on the screen. Everyone else can watch.
3. Pick whether a hit fires again, the time per shot and the time to place ships, and start.