Due to, i believe, the order of events being processed, it can feel like a very long time between researching a weapon upgrade and seeing the effects of that upgrade applied.
For example, in the attached save below, the following events occur:
- On Turn 12, Mass Driver 2 is researched. A fleet sits in supply awaiting the upgrade, so that it is prepared to engage a sentry, which sits guarding a system one jump (but two turns) away. If the fleet departs on Turn 12, it will not upgrade before the battle with the sentry.
- Now my understanding of the mechanics (some of which i believe have changed recently) is somewhat hazy, but, i believe on Turn 13, the effects of Mass Driver 2 are "active". The display at this point still shows that ships have MD1, but if the fleet departs on Turn 13, the upgrade to MD2 will occur "midflight" in time for the battle.
- If we leave the fleet where it is, on Turn 14, the fleet actually upgrades to MD2 fully (the display has updated to reflect that the ships have the MD2 weapon value of 4).