How to Play a Naval Duel for Two on One iPhone (and Beat Captain Rojo)

The paper version of this game needs two grids, two pencils and a book standing up between you so nobody cheats. On a phone the grids are easy. The hard part is the secret. Both fleets live on the same screen, so the game has to let you look at yours while your rival can't.

That's the problem Peekaboard solves, and this post covers how a naval duel works on one iPhone, how to keep your fleet hidden, and the tactics that actually win.

Disclosure: I make Peekaboard at Applestan. It's a free download for iPhone with iOS 27, it came out on 13 October 2026, and its first game is Naval Duel. Everything below matches version 1.0.

The board and the fleet #

Each player gets one half of the sea, a grid of 10 by 7 cells. That's 70 cells to hide in.

Your fleet has five toy ships, 17 cells in total:

• a carrier, 5 cells long
• one ship of 4 cells
• a cruiser and a submarine, 3 cells each
• a destroyer, 2 cells

You take turns firing at one cell on the other half. A shot is a hit or a miss, and when every cell of a ship has been hit, it sinks. The first player to sink the whole enemy fleet wins. A hit does not give you an extra shot, so it's always one shot per turn.

Two players on one phone #

Lay the iPhone flat on the table between you. Your half is the one nearer to you, and the other player's half is upside down from your side, the right way up for them.

Between turns a cover screen hides the board and tells you to pass the phone to the other player. On a table you can just turn the phone around. Either way, nobody sees a fleet that isn't theirs.

How to peek without giving anything away #

In a two-player match your ships are hidden most of the time, even from you. You check where they are by peeking.

On most iPhones you touch and hold the eye button in the corner. Your ships show on your half while you hold it and hide the moment you let go. Cup your other hand around the screen if your rival is the leaning-over type.

On iPhone Duo the idea is nicer. The phone lies open and flat between you, and on your turn you fold your half up toward you, like lifting the edge of a playing card. To be clear about where this stands, Peekaboard's fold-to-peek has only run in Apple's iPhone Duo simulator so far. iPhone Duo goes on sale on 23 October 2026, and I'll update this post after I've played it on a real one.

Placing your fleet #

Drag a ship to move it and tap it to turn it. Shuffle throws the whole fleet into a random layout, and Ready locks it in. In Peekaboard ships are allowed to touch each other.

A few things worth knowing:

• Mix directions. A fleet that's all horizontal is easier to read once your rival finds the first ship.
• Touching ships confuse people. Two ships side by side make a long line of hits that looks like one big ship. Your rival keeps firing along it, expecting a sink that doesn't come.
• Don't fall into a habit. If you always hide the carrier along the back row, a friend who plays you often will notice.
• Shuffle is a fine answer. A random layout has no habits at all. If you can't decide, shuffle until nothing looks too tidy and press Ready.

Firing: hunt first, then target #

Every good player switches between two modes.

Hunting is firing into open water while you haven't found a ship. Don't spread shots at random. Fire on a checkerboard pattern instead, only at cells of one color. The smallest ship is 2 cells long, so it always covers one cell of each color, and every other ship does too. That means you can find the whole fleet while firing at no more than 35 of the 70 cells.

Once the destroyer is gone, the smallest ship left is 3 cells long. You can then space your hunting shots three cells apart along each row, which needs even fewer shots.

Targeting starts with your first hit. Try the four cells around it, one at a time. When you get a second hit next to it, you know the direction, so keep firing along that line in both directions until the ship sinks. Then go back to hunting.

If a line of hits keeps going past the length of any ship you still have to sink, you've found two ships touching. Work out where one ends by trying the cells beside the line.

Playing Captain Rojo #

On your own, choose You vs Captain Rojo and pick a level. He plays fair. The computer only knows what you would know in his seat, which is where his shots hit and missed, never where your ships are.

The three levels play very differently:

• Deckhand fires at random cells. He doesn't chase his hits, so a good hunting pattern beats him easily. This is the level for a first game or for kids.
• Captain plays the way this post just described. He hunts on a pattern based on the smallest ship you have left, then fires around his hits and finishes lines of hits. To beat him, you need to hunt better than he does, because he won't waste many shots.
• Admiral counts every place each of your remaining ships could still fit, given his hits and misses, and fires at the cell that the most of those positions cover. Cells near the middle of the board can be part of many more ship positions than cells along the edges and in the corners, so early on he aims at the middle.

Against the Admiral, ships along the edges and in the corners tend to last longer, because fewer possible positions cover those cells. It won't save you forever, since he narrows things down with every miss, but it buys you shots. Just don't use the same trick against a friend who reads this post.

A quick checklist #

• Lay the phone flat between you, and hold the eye button only when you need to check your fleet
• Mix horizontal and vertical ships, and let a few of them touch
• Hunt on a checkerboard, then switch to every third cell once the destroyer sinks
• After a hit, try the four cells around it, then follow the line
• Against the Admiral, use the edges and corners

Peekaboard is free, with no ads, no account and no Wi-Fi needed, and a match saves by itself if you have to stop halfway. Naval Duel is the first game, and more games for two will come to the same table. See Peekaboard.