Is Swords & Spells supplement V?

My 6th print is not. The 3rd/4th print on the Acaeum isn't either, but I'm sure you already looked there.

Yeah my take on it is that it was a failed replacement for the Chainmail combat system. Those whose characters survived long enough to command armies were happy enough with what they already had (if they didn't just use houserules or other wargaming rules anyway).

Of course, the AD&D 1e DMG refers directly to Swords & Spells on several occasions when referencing rules.

Philotomy, my apologies. This thread fell off of my radar very quickly and I never got back to you. There is a reference to Swords & Spells on page 66 of the AD&D DMG, under "Charge." I was sure there were one or two more, but am having trouble finding them.

One needs D&D for details of the fantastic elements that really make Swords & Spells stand out. From that perspective, one could see D&D as the "supplement."

The other notable aspect is its largely dispensing with dice-rolls. The Complete Brigadier is another game with a similar element -- something that might turn off a lot of people -- but I think it's been more successful partly because it was clearly aimed at historical war-gamers.

S&S was unlikely to get a chance with anyone not already a D&D enthusiast, and those worthies were increasingly uninterested in the big battle game. Eventually, Games Workshop found a hugely successful take in Warhammer (which was much more in tune with the aesthetics of the later fantasy game market).

In my experience, Chainmail is less demanding and so better suited to a more casual interest in that part of the hobby. Depending on one's priorities, S&S might be judged a better design -- but in my experience it has seen very little play. On the other hand, I have folded bits from it back into D&D.

The only part I'm using just now is the listing of spells, which includes data for area of effect, duration and the like not in the D&D books. For instance, Sleep is given a small (1" diameter) AOE -- but has more range -- relative to the later AD&D version.

In the past, I have also used:
the revised combat matrixes
weapon vs. armor modifiers not in Supplement I
the turn sequence
first strike rules
movement rules
missile rules
probably miscellaneous other bits and bobs that don't come to mind immediately

(I sometimes ran with a much less "stripped down" rules set than today.)

Swords & Spells is a new set of miniatures rules entirely and does not supplement Chainmail at all. In his introduction, Gygax claims that these new rules are better suited for playing mass combats with OD&D than are the Chainmail rules. It's easy to see why, since (to cite just one example) every D&D spell, including those from the supplements, is given stats for use in mass combat. Indeed, the overall terminology and mechanics draw strongly on OD&D.

So, in my opinion, it's a supplement to OD&D in all but name.