Phone: drag your finger, the boat follows it and keeps just above your finger so you can see it. A tap on the water or the FIRE button launches a torpedo.
Computer: the arrow keys ← → ↑ ↓ or WASD steer the boat, Space launches a torpedo, P pauses, M toggles sound, V switches the view.
The torpedo runs straight up while the ship moves: lead your target. A marker on the water shows the meeting point, and it turns green when the boat is lined up. The boat carries only three tubes: while torpedoes are in the water the next cannot launch, and the FIRE button dims. The deeper the boat lies, the longer they stay in the water.
Points for a hit and for a sunk ship arrive as a line in the right corner: nothing floats up over the water, so the aim and the ships stay visible. Points are used twice. Points won in battle grow your rank, which arrives as the same card in the right corner: another tube, a stronger hull, a two-torpedo salvo, homing, full speed. And after a run all the points you earned go to the shop bank at the top of this screen: there they buy gear and magazine tiers.
A sunk ship drops a boon: it sinks in the water, and the boat picks it up if you come close. Inside are double points, fast reload, a three-torpedo salvo, homing, full speed or a hull repair. What is active and how many seconds remain shows on the right under the buttons.
Each convoy gives a fixed number of torpedoes: the remainder shows at the top left. The allowance for misses shrinks with every convoy. A miss costs one torpedo, a salvo spends as many as it fired, which is why the magazine gives more for a salvo. What you save carries over to the next convoy, but no more than eight. If the torpedoes run out and the convoy is still afloat, the run is over: there is nothing left to sink with.
Points for a run go to the shop at the top of this screen, and there they are spent. Gear is bought once and stays aboard: other torpedoes, hull protection, boat looks, night hunt and storm. Below the display case lie the magazine and the shells: torpedo stock, another tube, torpedo speed, warhead power and a hull compartment. These tiers are bought one at a time, each dearer than the last, and they stack with rank and awards. What you buy goes on the boat at once, the price leaves the bank, and the total of points across all runs stays: awards are counted by it.
The magazine also grows with awards: two awards give four extra torpedoes, then faster torpedoes, a double magazine, a stronger warhead and a full arsenal. The whole ladder lies below, under the rank ladder.
The cruise has nine convoys, and each is heavier than the last. First: a destroyer and a battleship bomb you, one bomb each. Second: ships move faster, bombs fall in pairs, and cruisers join in. Third: the convoy is at full speed, bombs come in threes, the tanker bombs too, and some bombs home in on the boat: those are marked with a blinking eye and a pink ring. You can always outrun one, the boat is faster than its turn.
The nine convoys are split into three stages, three in each. The first stage is the Baltic, the second the North Atlantic: darker, colder water, two battleships in the convoy, more bombs and more accurate ones. The third is the Arctic: three battleships and no torpedo boats, lighter water with a green cast, and bombs come in threes with almost every one homing in on the boat. Between stages the battle stops, the panel shows the stage just cleared and what waits in the new area, and the base patches one hull breach. Clear all nine convoys and the cruise is done.
You can take the view through the periscope: an eyepiece frame, a reticle with marks along the horizon, a depth ladder on the sight, and depth and bearing readouts. It is presentation only, it does not affect the battle. Choose it under View at the top of this screen, open view by default. You can also change it in battle: on a computer with the V key, on a phone with the Periscope button on the pause plate.
Hits in a row without a miss build a streak: from the third hit points rise by a quarter, from the twelfth they double. The multiplier shows under the boat. A miss or a breach resets the streak.
Deeds in battle earn medals and orders: for a cleared convoy, for accuracy, for a cruise without a breach, for a battleship. An award arrives at once as a narrow card in the top right corner so it does not cover the aim, and the whole rack lies on this screen under the Awards button. A medal can be earned again in a new run, an order is given once.
Every convoy carries 10 ships, the fleet is the same as in classic sea battle. Destroyers and battleships drop depth charges, so get out of their path; anyone who passes by returns at the end of the convoy.