Tortoise

 This is the Tortoise, a British WWII super-heavy assault gun. Half a dozen prototypes were built, but its main intended purpose was smashing through fortifications like the Siegfried Line, and by the time it was ready, there was no longer any need for it.

This model is 1:100 scale (15mm), and was printed in PLA+ on my Ender-3 FDM printer.

eSun PLA+, 0.08mm layer height

I printed a second one, using Cura's tree supports, just to see how it would do. Apart from the stringing which seems to be an inescapable feature of this filament (brand unknown), it printed fine for the most part.

However, I cannot figure out at all how Cura's tree support placement algorithm works. You can see, under the gun barrel and along the bottom of the side-skirts, supports are clustered together in dense groups, and then there are long bare gaps.

With my printer in its largely stock setup, I can just bridge those gaps, but not completely cleanly. If the same number of supports had been spaced evenly along the length of the area to be supported, it would have printed much better.

Now, I'm impressed with anyone who can figure out this sort of programming wizardry to begin with, but I don't think it can be denied that the algorithm could do with a bit of refinement. It would be even better if I could manually add or delete supports in Cura; it's possible in another slicer app (Solidify3d), but that costs quite a large number of yankeebucks, so I'm unlikely to get a copy unless we win the Lotto.