Bryan McGrath is a retired naval officer and he makes the case thinking about the size and shape of the Navy through the primary lens of capability virtually ignores what the Navy spends the overwhelming amount of its time doing, which is acting (along with its land force, the Marine Corps) as the nation’s primary peacetime security force where its commercial and diplomatic interests lie—the overwhelming majority of which are proximate to the sea.
This can be stated as a enough gunboats for gunboat diplomacy and to police the world.
The critical peacetime role is overwhelmingly associated with being there, which is a function of numbers (capacity); numbers to carry out presence where it is desired, numbers to account for the great distances that our fleet must travel to be where desired, and numbers to account for the maintenance necessary to ensure the ships last for their programmed service lives.
The ships carrying out this presence mission must, of course, be capable of combat operations. This is the essence of conventional deterrence, in which would be disturbers of the peace are confronted with tough choices backed up by present, capable, combat power.