Operation: Siege is a mod for registered Wolfenstein, made by Celtor. It was released on July 8, 2000 and was listed as being a beta. No full version was ever released.
It features 7 levels of questionable quality, mainly very small in size. Certain levels feature a number of bugs, including guards not reacting to the player (as posted).
Graphics are borrowed mainly from DOOM, The Lost Episodes and Operation: Panzerschiff.
No coding changes were made, and as such the mod is playable in SDL.