That's not really true. It has to at least be plausible. Usually. One exception that comes to mind is a couple of patents some physicist working for the US N

That's not really true. It has to at least be plausible. Usually. One exception that comes to mind is a couple of patents some physicist working for the US Navy created that probably aren't real technology. Anti-gravity devices and the like. Why they admitted those? No idea, but possibly this was done as part of some sort of hearkening back to the cold-war-era strategy of 'waste the enemies resources on a goose chase' kind of thing.