It had four Pratt & Whitney engines - two under each wing.
All throughout WWII.
It has 8 engines, four on each side, two per boom.
On a B17 bomber the spent shell casings (brass) fell on the floor. Everything was scarce and rationed during WWII so I assume the brass was reused.
Europe
A Vickers Vimy IV bomber. It used two Rolls-Royce Eagle engines.
All throughout WWII.
B52 B1B B17 B24
perhaps you mean the 'flying fortress' a B17 bomber
Boeing B17
The B17, B24, and B29s were the heavy bombers of WWII. The B52 was the heavy bomber of the Vietnam War.
It has 8 engines, four on each side, two per boom.
A B-52 has 8 TF33-P-3 turbofan engines
It was the Flying Fortress, dubbed so by a Seattle journalist and later adopted as the official name.
B-52
Good aerodynamics and powerful engines.
Apart from the obvious increase in the number of engines, there is no real difference. The extra engines give increased thrust and thus additional "bomb" capacity. Depending on the role intended, a four engined bomber will be preferred as in a war, fuel is not a consideration.
Under the wings, Between the engines.