Unusual ordnance

[chris vickery]

I recently picked up what I believe to be an unusual piece of ordnance. Unfortunately at the moment I've no picture available to post. It is painted white overall. It appears to be a mortar or bomb of some sort. The rear section has 4 fins similar to a mortar or a bomb. What is different is that there is a plate affixed to the bottom end which protects the fins. The length is about 8". The front section has a flat cap threaded on it. It looks like some sort of propellant or explosive may go inside. My thinking is that it might be an illumination shell? Diameter is about the same as a beer bottle. On the tail fin is a number No.68 ATI/L 1942.Who's our resident expert on WW2 munitions? Any ideas?