They're not actually that small compared to other contemporary engines. Here's one being tested alongside the J57: https://en.wikipedia.org/wiki/File:Boeing_JB

They're not actually that small compared to other contemporary engines. Here's one being tested alongside the J57: https://en.wikipedia.org/wiki/File:Boeing_JB-52E_(SN_57-0119)_in_flight_061127-F-1234S-026.jpg https://en.wikipedia.org/wiki/File:Boeing_JB-52E_(SN_57-0119... The C-5 fuselage is quite big, so they look smaller than they are.