Tau forcefield thing?

Another thing for a friend at the club. This doodah was a lot of fun to paint. I did quite a bit of masking, chipping and loads of weathering. I think it's some sort of floating forcefield-bearing structure that advances across the battlefield. There's a big gun on a tower involved, too. The forcefield is a separate piece of translucent blue plastic that the friend who owns the kit has since inserted.