> It doesn't look like the waterfall model was ever used

Well - yes, it was used, and still is: it's the default if you're not careful or if you don't think very hard or realistically, or are very naive. The confusion is that is was only given a name to disparage it: W. Winston Royce observed that the way most people managed software projects was completely unrealistic and didn't take into account changing requirements. He called it "waterfall" as a way to underscore how inflexible the default "write down all the requirements, then write down how long they're going to take, then do them in that amount of time" approach was.

Unfortunately, most people who adopt what they refer to as "agile" processes are still stuck in that same mindset; they think that, by having daily standups, putting in JIRA tickets, and referring to every two weeks as a "sprint", they'll somehow meet the project manager's pipe dream of 100% predictable software development schedules.

Royce didn't set it up to disparage it. He set up his idealized flow and then proceeded to add details that he believed were critical to making it work. In the end, what he proposes is what most people understand to be Waterfall but with some extra details:

- Feedback loops (because problems or deficiencies will arise)

- Involving the customer (because you don't want to spend 12-60 months building the wrong thing)

- Build a prototype (good advice)

- Document, document, document (he thinks 1500 pages is a good target)

The only thing practitioners seem to have taken away is that last bullet. He still made a strong distinction in his model between analysis, design, and implementation. Though, to be fair, at the time "programmer" was more of a technician level and design often involved making detailed designs like flowcharts and such that could be more easily translated into code. These days, design and implementation are really tangled up, and the documentation is awful an non-actionable (I've been on those teams, it's nightmare inducing). People think prose can replace a diagram, so they fill out their 1500 page quota with lots of words but no clarity.

The name came later, and was enshrined in a DOD standard by people who couldn't read past the first few pages. So they entirely missed the lessons learned he was trying to apply to it.

Agreed. Pure waterfall has become a strawman for the Agile zealots. Realistically, Waterfall is used as one component of the overall design and implementation process.

The waterfall model is definitely used at scale in DOD projects. It is as horrifying as it sounds.