Why are warships harder to stretch than airliners?

Why can airliners gain or lose fuselage sections more readily than warships?

Ships can be stretched, but hull curvature, strength, loading, stability, and hydrodynamics make the change more complex and politically unattractive.

Modern BAE designs such as Type 26 can include a planned insertion point, so naval architects can stretch a warship when the requirement is anticipated. Governments remain wary because the joint can raise concerns about longitudinal strength and because added volume changes loading and stability. A ship's hull also curves and changes section along its length, unlike the comparatively regular tube of an airliner fuselage. Moving or inserting a section therefore alters displacement and how the hull passes through water, as well as internal floor area. This geometry allows warship families to share a design while making fuselage-style length variants difficult to standardize.