Off the top of my head I42, a DSO normally requires some element of command or leadership to be exceptional, above and beyond etc etc, and is a "wartime only" award.
It was also (the DSO) considered at one time as a "just missed a VC" award, but since 1993, that role has been taken by the CGC (Conspiculous Gallantry Cross).
Up 'til that point the DSO was an "officers only" award; since then, in theory at least, it can be awarded to all ranks, but no non-commissioned awards have yet been made.