how can this be done?

EVN is set up so that, at some point new ships become available, appearing in both the shipyard, and as randomly appearing ships in a system. Both the RAGE gunboat and the Zephyr fall into this category. I want to do something like this, but a little more ambitious.

I want to have a government that uses a fighter, the F1. This fighter is found patrolling its systems, and also found aboard the government's carriers.

At some point I want the F1 to be replaced by the F2 (and later the F3 and F4). At this point I want the F2 to appear as a new patrolling craft in the government's systems, as well as aboard the government's carriers. The trick is, when the F2 is released, I want all F1's to go away.

Obviously the F1 and F2 will have to be different ship resources. So will the F1 amd F2 fighter and fighter bay outfits. The carriers that carry the F1's and F2's will also have to be different variants of the carrier. I can control the F1 and F2 availability in the shipyard, hiring an escort in the bar, outfit fighter and fighter bay, all by using the availability fields and bit sets.

What I don't understand is, how can I make the F1 stop being the regular patrol craft in a given system, and have it replaced by the F2? I'd like to swap out carrier variants at the same time. I suppose I could make mutally exclusive system resources for every variant of the F-series, but this seems rather tedious.

I can't just copy what was done with the Zephyr/RAGE gunboat because in both cases, the ship was just a new ship. It appeared as a random flying ship, but it didn't actually replace the appearance of another ship.

Is there another way to do this, other than creating different mutually exclusive masking system resources, each loaded with different dude type resources for the various F series fighters?

You can set the AppearOn and Availablility fields or the F1 version of the fighter and the carrier no longer to be true one the F2 has been introduced. Say you mark the introduction of the F2 by setting the ncb b5372. You would put "b5372" in F2 stuff, and "!b5372" in F1 stuff. Putting a ! negates the bit, i.e. the expression will only be true if the bit is NOT set if negated.

If then you plan to add the F3 and F4, then it is a little more complicated. Say the F3 is introduced by the ncb b5373. The F1 has already disappeared, no problem. Now the F2 has to disappear as well. So you have to put in the ncb test fields of F2 stuff: "b5372 & !b5373". This expression will be true when b5372 is set AND b5373 in NOT set. Then supposed F4 is introduced by b5374, then the ncb test fields of F3 stuff has to contain "b5373 & !b5374" and the ncb test fields of F4 stuff has to contain "b5374".

Is that clear enough?

I think so.

Are these "Appear on" and "Availability" fields on the ship resource, or the dude resource? (I'm at work and not near EV NEW right now).

My goal is to have whichever is the current model fo the F series to be patrolling my government systems.

If dude 128 is the F1, and 129 is the F2. Do I put both in the system resource and EVN will be smart enough to not have dude 129 appear until the "appear on" and "availability" bits are set correctly?

Am I being clear?

You could have the F1 and the F2 in the same düde. Set each one's probability to 100%. This won't give you problems, as the variants are mutually exclusive.

That way, you don't have to swap the s˙st, or use too many düdes.

The AppearOn and Availability test expression are in the shďp resource. Read about it in the topic just down (the shďp annotated template).