The high Cold War US Navy provides an alternative parallel for Starfleet: a small group of the newest designs operated alongside ships retained for a long time. Large navies could sustain that mixture of new and repeatedly modernized hulls. Shipbuilding cuts during the 1980s and early 1990s, cancelled peace-dividend orders, and sales of existing ships reduced the number of hulls available. Royal Navy terminology distinguishes commissioned ships needed for current operations from ships in ordinary, which are maintained without active use. Keeping ships in ordinary preserves hulls for when they are needed.
Notable Point · 8:24-9:55
Why ships in ordinary preserve fleet depth
A fleet can combine new designs with long-serving hulls, while ships maintained in ordinary remain available beyond current commissioned strength.