OK, let's try to make it simplier, not more complex.

There are planets that allow (nor produce, more like allow a percentage of population to be recruits) a certain amount of CREW, you also have many SHIPS. Ships require crew to operate. Typically you will have much more ships (most of them old) than available crew, therefore in practice you will have almost unlimited reserve of inferior ships. How to make it work?

For example the player gives an order to keep the ratio of:

5% - recon ships

10% - capital ships

70% - destroyers

15% - support ships

The HeadQuarters AI will assign the ships from the reserve pool to meet the proportions as similar as possible assigning the best ships first (for example there is enough crew to man 100 ships (so 70 destroyers since that's the proportion) and there are 40 Destroyer II and 150 Destroyer I available, the ACTIVE FLEET will have 40 Destroyer II and 30 Destroyer I.

But then there is a battle and 5 Destroyer II are destroyed, so the current composition is 35 Destoyer II and 35 Detroyer I. But that's unrealistic and not very playable since the total military numbers have not changed, the crew that was lost is still there? And should these new ships from reserve be added immediately to the active fleet?

This is giving me a bit of headache :D

What you think about this?

* significant delay when switching ships (for any reason, could be because the original ship was detroyed (but crew survived) or to man a new ship or to switch to a better ship)

* discourage big ships reserve by maintenance cost

Details:

- whenever a crew is assigned to a ship it takes 3 turns before the ship become operational

- the player can set a "Military readiness level", when it's set to low then up to 20% of crew can initiate switching ships each turn (best during peace since it can cause a significant part of the military being locked in the switching state), when it's set to high up to 1% of crew can switch ships (best during war but you can't effectively upgrade to new ships since the new ships will be manned very slowly). All these numbers do not affect unassigned crew, all of them can be assigned at once.

- you pay maintenance for fleet. For active fleet you pay 100%, for reserve fleet you pay 50% but a portion of reserve fleet has a free maintenance (so the player is encouraged to keep some older ships but not too many). The player can scrap ships anytime.

Command and control is usually the main scaling issue - can units even communicate sufficiently assuming some commander is capable of coordinating large numbers of ships (usually theiris a hiearchical command structure with group entities to facilitate control AND default orders to handle situations when the command structure breaks down