Even more interesting; probably the biggest techonolgical secret this country ever had was the 1970’s-80’s “Chevaline” project. This was a UK-designed mid-life update for the Polaris nuclear missile. These days you can find endless pages about it via Google. But at the time, it was most secret, mainly because successive Governments hid the huge cost (mostly over-spend) from Parliament for the best part of a decade. Only Mrs T had the nerve to finally make it public.
There’s an overview here
https://en.wikipedia.org/wiki/Chevalineand some pictures here
https://fas.org/nuke/guide/uk/slbm/chevaline.html. Unfortunately no clear pictures of the electronics, but discrete components on solder-tag boards were predominant. It's important to recall, this unit was effectively a fully stabilised spacecraft, albeit one which spent a very short time in space!
It was replaced by Trident around about 1992 and many people were “a bit surprised” that a number of the Chevaline vehicles (minus their shrouds and fully exposed as in the pictures above) were soon put on display in museums (I was there on the first day they were on display). After some months, however, these were hastily withdrawn from display, had various bits removed and then returned to the museums. Of course, these days, we just buy stuff from overseas.
B