Why submarine size depends on era and mission

What are the ideal displacement ranges for different submarine types?

They depend on era and role, with coastal, oceanic, minelaying, and modern strategic submarines each requiring a different size.

No single sweet-spot tonnage works across submarine history. Coastal boats, ocean-going submarines, and minelayers each balance range, payload, and operating area differently. Modern nuclear boats must also carry sensors, habitability, weapons, and strategic systems that drive displacement upward. For contemporary ballistic-missile submarines, the Dreadnought class sits near the appropriate design point for its mission.