Youtuber MOS6510 has posted some videos of the new Airfix 1/24 scale Spitfire imcluding a presentation by the designer. If you ever wanted to know how a kit is made this will be informative. He describes how he went from a set of plans to the kit parts.
https://www.youtube.com/watch?v=d_4atLsMSLM&list=PLc2bfNWiJAEmMQ7AaueWzBcE2CLHB8G_9&index=5
The video is an hour long, but he describes the process. It was a pandemic lockdown WFH job that tool him a year. It would be similar for any project; aircraft, armor, ships. autos, etc. The only difference might be the scale. The larger the scale the more details expected and included.
Noted in passing that the 400 plus parts were sent to a 3D printer so that assembly issues could be worked out. It also helped in preparing the instructions.
In a second video he presents the injection molding process. Airfix's contractor is a full service shop that takes the CAD files produced above and cuts the steel, makes test runs for QC development, does production, more QC, boxing and shipping. Decals are printed by another contractor.
https://www.youtube.com/watch?v=QW1EaiPpbWU&list=PLc2bfNWiJAEmMQ7AaueWzBcE2CLHB8G_9&index=1
Interesting to note that the production rate is about 90 units per hour
EDIT:I tried to imbed the video, but no joy.