The B-47 was a beautiful plane but pretty underpowered. Consider this - the B-47B's takeoff weight was 184,900 pounds and all six engines put together generated 34,800 pounds of thrust, about the same as each of the engines on the YF-22 Raptor. BTW: that was a huge improvement over the XB-47 prototype that weighed 162,500 pounds and only had a total of 24,000 pounds of thrust. By comparison, each engine on an F-15E puts out more than 23,000 pounds of thrust with half the takeoff weight of the XB-47.

Low takeoff thrust is why so many B-47s used rocket assisted takeoffs. That was a capability added to the B-47E model, a plane with a takeoff weight of 220,000 pounds and jets that produced a total of 43,200 pounds.