Why submarines are easier to define than surface ships

A submarine is a concentrated attack capability rather than a platform expected to conduct every peacetime and wartime mission. That narrower purpose gives designers a clearer starting point even though pressure-hull engineering remains difficult and expensive. The choice between torpedo-tube launch and a separate vertical-launch system still matters: VLS adds size and complexity, but it prevents land-attack missiles from consuming magazine space needed for torpedoes and decoys. Surface combatants face a wider argument over short-range single-purpose launchers versus deeper, strategic-length cells able to accept several weapon types. Their much broader and less predictable mission set makes replacement and upgrade paths harder to settle.