In my experience it never worked. We were able to achieve success only by secretly ignoring the rules and process and instead developing software in what detractors called a "cowboy" process. When "agile" came out, it changed our lives. We adopted a few new good ideas, but mostly kept working as we had been. But now we could point to this quasi-official "agile process", with tailoring as they recommend. As long as we were following a process, and not being "cowboys", folks seemed satisfied.
These days the Air Force has caught on to "agile". They even have 400-page manuals on the process to follow to be "agile"! We still cut some corners here and there and do what we think makes sense, but there's far less process push-back than there was in the past.