After a certain number of kills (below 8) you can spawn a cannon, which can be operated by 1 person.
Basically it shoots 2 round a second, has the blast radius of 2 grenades, the same damage&Shrapnel as a grenade, and has 60 rounds (30 seconds of glory)
If this is implemented, then players won't have to constantly reload their grenades, and charge through large, open maps only to get shredded to cheese by sum-machine gunners and riflemen, and then turned to swiss cheese by shotgunners. This should be 1 kill below airstrike (spree incouraging), so it's not too common, but it still is easy to get, and now players will be able to offer front-line support to their buddies.
Downsides:
is fixed place, can be destroyed in 2 SMG clips, 2 Rifle clips, 6 shotgun bursts 3 grenades or 1-3 rockets (assuming those come out).