A-10 Warthog

[Urbane Guerrilla]

The backpack engine location is for blanking off the engines from likely angles of ground fire, etc. as Bruce said. The engines's exhaust signature is also blanked by vertical tailplanes outboard of each exhaust stream, as well as the horizontals. The engine access for maintenance is good so a bashed engine may be readily changed out, the fuselage is freed up for fuel tankage for loitering endurance and as you noted the wing structure only has the job of carrying abundant external stores without having to carry engines as well.

And the plane is designed to soak up 23mm all day. The type has a couple of air-to-air victories with that big gun: two helicopters over Iraq. It could dogfight in a turning fight once the external stores are pickled off the wings, but only with aircraft that can't go much faster than 400 knots.

I've heard 20mm M61 type guns fired. It is the scariest single sound I know. A loud, cracking, blasting ripping noise nearer the sound of an air hammer mixed with a chainsaw and tearing canvas than a machine gun.