Why interplanetary warships resemble submarines

Would future space combat be more like submarine warfare than air combat?

For interplanetary operations, yes; isolation, endurance, and self-contained life support make the submarine analogy stronger.

Combat inside Earth's atmosphere or near-orbital space could retain some features of aircraft operations. Interplanetary travel creates a different problem: a crew remains sealed inside a hull for months and cannot simply leave when machinery or living conditions fail. Food, life support, repair capacity, and every other necessity must travel with the vessel. Those endurance and isolation demands make a submarine a more useful naval analogy than an aircraft for a long-range spacecraft.