Ron,
As James said this one is the Avro Shackleton Mk2 Phase 3 and you are looking at the twin Hispano 20mm cannon. The same installation was also fitted to the Mk3 Shack along with a pair of Viper jet engines and tricycle undercarriage instead of being a tail dragger. The cannons were visually aimed via the electric Boulton Paul Turret Gunsight. A total nightmare to operate and difficult to loose off more than a few rounds before it jammed.The engine you can see is a RR Griffon with contra rotating propellers. Incredibly Noisy. Sitting in that gun position on flights 'up north' was so cold we would wear and immersion suit and up to three cold weather artic parkas with another one over your knees as the wind used to howl in through the gun shrouds. It could also be configured with tracer and D/U rounds if required - God forbid. That was a photo of the Cockpit above - the tatty black one.
Incidentally "avro" and a number , ie "Avro 7" is still the r/t callsign for Woodford based test crews where the Shackleton was built.