The M15A gun motor carriage was a WWII era design for an anti-infantry vehicle. Apparently the idea was it could fire in all directions without having to take the time to traverse a turret. I haven't been able to find much else about it, aside from the fact that only one prototype was ever built.
Looking at it, I'm surprised they even wasted their time and money building one of the things. Aside from the fact that it would have been a sitting duck for any enemy tank it encountered, I wonder how much ammunition it could have carried? Whatever the amount, the large number of guns it mounted would have buzzed through it in short order.