self-propelled_gun, tank_destroyer, turretless_tank
is there really a major difference in these terms at least for tagging purposes? should we settle for the most general term and alias the all?

The way I look at it, these three tags together cover the following categories of armored vehicle:

-Self-propelled howitzers (e.g. M7 Priest, AS-90)
-Gun-only air defense vehicles (e.g. M163, Gepard)
-Assault guns (e.g. StuG III)
-Turretless gun tank destroyers (e.g. Jagdwhatevers)
-Turreted gun tank destroyers (e.g. WWII American and most modern designs, like the B1 Centauro)
-Missile tank destroyers (e.g. 9P157 Khrizantema-S, M901)
-Turretless tanks (as far as I know, this category consists of just the Swedish Strv 103, because Sweden insists it's a tank)

I'm going to ignore the air defense vehicles - some sort of "anti-aircraft_vehicle" tag would alone be able to cover them, gun/missile (Tunguska) and missile-only (Roland) anti-aircraft vehicles together in a far more sensible way, without getting these tags involved.

The existence of turreted and missile TDs means that tank_destroyer can't really implicate/alias either turretless_tank or self-propelled_gun - some have turrets, some don't use guns. turretless_tank is currently being used inaccurately anyway (assault guns/TDs aren't tanks), and using it accurately would restrict it to just the Strv 103 and make it fairly pointless.

What I would personally argue for, then, is this:

create alias turretless_tank -> self-propelled_gun

Which would leave only self-propelled_gun and tank_destroyer. SPHs, assault guns, and the Strv 103 would use self-propelled_gun only, missile TDs would use tank_destroyer only, and gun tank destroyers would use both. I think this would make tagging somewhat simpler and also more accurate, while not leaving anything out.

Thoughts? If this sounds good, I can go through those pics tagged with turretless_tank and add the tank_destroyer tag where relevant in preparation (there's only 38 of them). If not, I'm open to further discussion, of course.

Edit: Another option, which would be simpler but less useful for finding images, would be to fold everything into self-propelled_gun and relegate missile TDs to some kind of generic catchall "armored_vehicle" tag.

In opposition to trying to lump turretless_tank into self-propelled_gun. The point of the tag being created to begin with was due to their visual similarities to each other, tagging them based on their purpose means you're then crowding those that are dissimilar into appearance from each other under one tag and forcing having to perform a rather indepth search to find these vehicles that have a similar casemate design. Additionally trying to lump them by purpose doesn't make sense when you can have fictional turrentless vehicles and you'd then have to make pure speculation on the purpose of the vehicle to put it under a tag like tank destroyer. Additionally going with your proposed tank_destroyer and self-propelled_gun only tags you'd be lumping post #1356683 with post #1381721 and no means of separation besides sifting through the images, though the first post is more similar in design to what you'd be lumping under tank_destroyer.

Additionally only using self-propelled_gun would flood out things like post #1381721 and would deny the ability to easily find things like it from amongst the turretless designs.

If anything the turrentless_tank out of the 3 tags is the best defined tag as it is a visual based tag on the vehicles style unlike the other 2 which are purpose based tags and thus require background knowledge of the vehicle in question.

That's fair enough. I personally don't think requiring background knowledge of the vehicle is necessarily a bad thing in the case of real vehicles, but I see where you're coming from with fictional ones - I hadn't thought of that at all, admittedly.

post #1381721 and the like would be easily solved with a self-propelled_howitzer or self-propelled_artillery tag, though. I'm still not a huge fan of the technically inaccurate turretless_tank name, but there isn't really a better option I can think of that encompasses all casemated gun vehicles, plus the wiki explains it.

More to the point, though, I don't think either tags based on purpose or based on visual similarity can do it alone. Tags based on purpose by themselves can't handle vehicles, especially fictional ones, whose purpose is unknown or unclear, and of course they don't allow searching by visual similarities. (I look at it, it has a casemated gun, but I don't know if it's a TD or assault gun - without the turretless_tank visual similarity tag, I can't put it anywhere more specific than armored_vehicle). On the other hand, tags based on visual similarities by themselves don't lend themselves well to tag names (tank is based on purpose as a specific type of AFV - what do I search for to get an armored vehicle with a turret with a big tube sticking out of it?) and of course don't allow searching by the vehicle's purpose, which some people like me do want to do (my search is now spitting back tanks, turreted TDs, self-propelled mortars [like the 2S31 Vena], self-propelled howitzers [Palmaria], CEVs [M728], anti-aircraft vehicles [Otomatic], IFVs [BMP-3], and more [M113 FSV] at me, none of which I care about except actual tanks.) Removing either set leaves us in a bit of a spot.

Which leaves us here with 1 tags based on purpose, 1 based on visual similarity, and 1 (self-propelled_gun)where I'm too tired to figure out where it belongs, if anywhere. If we accept that purpose tags and visual tags can't really replace each other, that just leaves what to do with self-propelled_gun - split its members into more specific tags, keep it as a catchall, something else?

I apologize if I'm not making any sense and for trailing off without any proposal at the end; it's late and I'm tired and I've probably thought more about this than what I'm actually supposed to be doing tonight...