I work in State government, which in our state is traditionally waterfall in practice. I've brought up trying to do some DevOps but it has met with resistance. The single, most important thing, to the way we handle things is that any and every project must have a very detailed, exhaustively written Requirements Document! That Requirements Document is the Word of God! And if it takes 9 months to finish a requirements document, so be it. Even though I've been in this position for almost 2 years I still don't entirely grasp all of the reasons why the Requirement Document is So All Important. I've had various guesses as to what the reason(s) is(are), but I really don't entirely know. I understand that even agile software development allow for writing a requirements document, but that it doesn't insist that it must be as completely detailed and filled out as the department I work for demands.
The result of insisting that a requirements document be as detailed as we require is that often the users making requests of us to do something, can't wait around for as long as this process takes. So they go off and do their own thing, resulting in even more headache and trouble for us. But who can blame them. There aren't many places that can wait a year before someone is allowed to open up Visual Studio and start writing the app.
Kindest Regards, Rod Connect with me on LinkedIn.