Spring RTS Engine

Hey,
I remember some months ago I did accidentaly used a "FPS mode on a unit" with controls with keyboard for move 'n all. I don't find it anymore. Was it a plugin or something removed, or the key changed ?

It's permanently disabled because commands given in FPS mode don't pass through luarules. As a result, it's unable to interact with all of BAs "normal" gadgetry and was a constant source of hacky code and exploits.

Argh, althought it was not of any use, it was awesome to feel being with the unit.
Nothing can be done to get the same feeling now ? What version of Spring should I get to use this view again ?

You can /cheat and to still use it, iirc. But it's not bound to a key anymore, so use /controlunit with the unit you want to fps selected.