Okay, undeliverable in the same sense their tanks are by air. Sure, you can load a T-34 (which looks like it also comes in at 27 tonnes) on an aircraft, but it's not intended as a scalable way to use them. You'll remember the plane was almost knocked out of the sky by the blast as it flew away. It was also the only model they had that could do it, and it couldn't go very far with such an unusually heavy load.

The largest nuke that saw actual service was the 25 MT American B41, which had impressive yield for it's size, despite, as you can see in the wiki's picture, still being a very significant device. There was also a project to design bombs of unlimited yields, but the scientists were basically just goofing off, and the army told them to stop it.

The modern Western (and Chinese?) design is at the other end of the space - being as small as possible while maintaining efficiency. They have just enough of a fusion stage to support full burnup in the fission stage.