- 💣
Torpedo: one per turn, and it ends your turn. It's the only way to sink ships, and a miss wastes the turn.
- 〰
Zeno probe: as many as your energy allows, each costing N. A photon starts in |0⟩ and is turned towards |1⟩ in N small steps of π/2N, passing the cell after each step.
- ○
Water: nothing disturbs the photon, it ends up in |1⟩, and the detector says "empty". This is always safe.
- ◆
Ship: each pass is a measurement. Usually it knocks the photon back to |0⟩, the quantum Zeno effect, and the detector says "ship" although nothing touched it. This happens with probability cos²ᴺ(π/2N).
- !
Absorbed: with the remaining probability the ship absorbs the photon. You still learn "ship", but the enemy notices you: alarm +4.
- ⚠
Alarm: the enemy fires 1 shot per turn, plus 1 more for every 4 points of alarm. The alarm cools down by 1 each turn.
- N
N = 1 is a plain classical touch, absorbed every time it finds a ship. Large N is nearly invisible but expensive. This is the Elitzur–Vaidman bomb tester.