User blog comment:Damac1214/Tons of Call of Duty: Black Ops III info leaks - 2 Days til Full Reveal/@comment-164.127.217.147-20150425112118/@comment-24756040-20150426120807

Well, even at the very start, Call of Duty's engine was just a Quake 3 engine, modified so severely that it bears little resemblance.

Skip to today, and I bet it's damn near impossible to find resemblance.