When I worked, I was employed by a large bank that employed 260,000 people.
Our migration from Windows XP to Windows 7 took three years, and involved tens of thousands of custom applications and vendor products. It was very painful for everyone, and cost hundreds of millions of dollars.
I worked a bank gig as well for quite a while doing S0laris/HPUX —> linux migration. I know of what you speak (our price tag was a bit less however; we had 1200 UNIX machines to migrate off of and it was mostly DB hosting).
I worked with a UNIX SA who did 8 years in the Navy supporting HPUX. The guy was sharp as a razor and entirely trained by the Navy. I have faith in them..
This has been repeated almost everywhere in the corporate world.
The question is: why hasn't the Navy been on top of this? The end-of-life for Windows XP has been known for years, and expected for long before that.
Yeah, I seen similar horror stories. I have also seen migrations to Linux (small insurance firm) that was far less painful.
Yeah, I migrated my business to Windows 7- 4,000 employees and it took us over a year. 300 applications many of which I had to repackage myself to work on 7.