Heavy Damage: When to Retreat

The rule: if any ship is heavily damaged (大破, Taiha) after a battle, choose Retreat (撤退, Tettai). Advancing with a heavily damaged ship is the only situation in which ships have been confirmed to sink.

What's safe: your flagship can never sink, and a ship that wasn't heavily damaged when a battle started is protected from sinking for the rest of that battle — including the night battle at the same node.

Why it matters: a sunk ship is gone permanently, along with its levels and equipment.

When a hit would take a ship's HP to zero, the game often replaces it with a smaller hit instead. Who gets that protection depends on the ship's state when the battle starts:

1. 1Look at every ship's damage label on the result screen, not just the flagship.
2. 2If any escort shows 大破, choose 撤退 (Retreat). Don't advance “just one more node”.
3. 3Night battle at the same node (夜戦, Yasen) is decided by the state at the start of that node's battle, so it's not where ships sink — but it does add damage and fatigue, so skip it on normal nodes.
4. 4Repair (入渠, Nyūkyo) before the next sortie. A ship that starts a sortie at moderate damage reaches heavy damage much more easily.

1. 1Advancing because the next node is the boss. This is exactly the case where ships sink. Retreat and try again.
2. 2Assuming moderate damage is always safe. It's safe from sinking at the next battle, but a moderately damaged ship can drop to heavy damage there and then must retreat.
3. 3Sortieing red-fatigued ships. Their protection leaves them at 1 HP, so they reach heavy damage far more often. See Fatigue and Sparkling Explained.
4. 4Closing the game mid-battle to avoid a bad result. The result is already decided once the battle starts, so this doesn't undo damage.

Can my flagship sink?

No. The flagship is always protected, even when heavily damaged. But if the flagship is heavily damaged and has no Damage Control, the game shows 「進撃が困難です」 ("advancing is difficult") and sends the fleet home automatically — and a fleet with a heavily damaged flagship can't sortie, exercise or go on expeditions until you repair or swap it.

Can a ship sink from full HP in one hit?

No — a ship that isn't heavily damaged at the start of a battle is protected. A big hit can take it straight to heavy damage, but not sink it.

Is a night battle risky for a heavily damaged ship?

Protection is set at the start of the battle at that node, so a ship that wasn't heavily damaged then is still protected in that node's night battle. The risk comes from advancing to the next node.

Why do some small ships reach heavy damage so easily?

When protection kicks in, the replacement hit is a fraction of current HP rounded down. For ships with low max HP, a max HP that's a multiple of 4 makes landing in the heavy-damage band slightly more likely. Large ships barely notice this.