Navy Fleet Battle is an Android version of Морской бой, the sea battle game played on squared paper across Russia for generations. It follows the classic Russian rules exactly, with no variants and nothing to configure.

Two ways to play:

- Against the computer
- Two players, passing one device between them

The rules:

- A field of 10 by 10 cells, ten ships, twenty cells of fleet
- Ships stand in straight lines and may not touch each other, not even at the corners
- A hit earns another shot, and the turn passes only on a miss
- Sinking a ship marks the water around it automatically, because no ship can stand there

Made to be handed to a child:

- Large boards and touch targets a small finger cannot miss
- Every shot is aimed first and fired second, so a stray tap costs nothing
- The outcome of a shot is revealed by its animation and never before it, on both sides of the board
- A sinking plays as two beats: the hit lands first, then the hull goes down
- The end of a game is shown as a picture as well as in words, so a child who cannot yet read still knows who won
- A hand-off screen between turns leads with a large player number, so the device changes hands without anyone reading anything
- Sound throughout, with a mute button on every screen that remembers its setting

Russian and English, changed with a button in the corner at any moment, including in the middle of a battle. The board is lettered in the alphabet of the language in use: А Б В Г Д Е Ж З И К in Russian, A to J in English.

Navy Fleet Battle is free and open source under the MIT licence. Every sound in it is a public domain recording. There are no adverts, no trackers, no accounts and no network access of any kind, and the app asks nothing of the system: no storage, no location, no camera, no microphone.