I felt sure there was a longish thread on loopy weapons too, but also can't find the damned thing.
Mind you, every issue of
Modern Mechanix seems to have two or three of the things that never left the dreamy minds of those that thought of 'em, so some examples that actually left the drawing board might be nice:
Does the Vickers beetle from the end of this one count? :
tele tanks
or is that just raw copy-cattery?
I'd nominate 'Nellie' as right up there.
To quote myself from 'elsewhere':
"Naval Land equipment' or Nellie the Trench-digger. Envisioned in this 'smaller' style named 'The Private' for infantry (Seems 5 were actually built...) and a larger 'officer' model for vehicles to follow. The intention was to dig deep trenches (sub-ground speed: 1mph) towards the enemy trenches when the 'inevitable' first war style of warfare that was envisioned (by a very few 'old gang' oddballs) began. Incapable of digging any soil other than particular French Loams it took an entire company of engineers to assemble, 3 separate loads and a fleet of lorries carrying just the track-plates.
In technical innovation, it was apparently a major achievement, but militarily, and in terms of usage of production capacity... oh deary me."
I have better pictures 'somewhere', but in the meantime this from Doug's Heavy metal gallery will have to do:
And of course, the 'Great Panjandrum', though that probably goes without saying

.
Cheers,
Adam.