I checked my old 1.11. game and I have designs of ship that surrendered in Class Design available. Maybe some new bug introduced in 1.12.?

I had no surrendered ships yet in my 1.12. game. However, ships that I captured with boarding are shown in Class Design correctly.

See post above.

I have no idea why it took an action to design a new ship but as soon as I started the captured designs showed up.

Edit: Spoke to Soon! Had to leave the program for a couple of hours and when I got back they had gone again! Frustrating.

Edit 2: Found them again, they are now in obsolete ship designs, even copies stay in obsolete designs.

Try checking show obsolete ships.

Tried that no effect

Edit: I just started designing a new class and low & behold the captured ship designs just showed up!

For the first time ever I have enemy ships, both commercial and warships surrendering before I have conquered the alien race. I have had an orbital miner, a couple of troop transports, a heavy cruiser and almost all a task force consisting of 7 strike cruisers, 3 escort cruisers, 3 missile destroyers and 4 escort destroyers surrender. All well and good.

However, only the orbital miner appears in my ship design tab. I suspect because that is the only ship type I had not designed. While I can overhaul and repair the other ships I really need to refit the others to bring them up to my fleet standards as I am in a hot war and very short of ships. Fortunately I have intelligence that the aliens are also involved in another war which has made them behave very strangely. But there is no entry in the ship design tab to work off although of course I have the full specs of the vessels. It also means I have no idea how to specify the missile load-out of the warships.

In a similar vein I also cannot recover a stock of precursor AAMs I captured, but apart from the entry in the planetary stockpile they are invisible.

Any ideas gratefully received.

Ian