You're exactly right. But as you suspect, there's reasons why you wouldn't want to do that in all cases. Turbojets derive all of their thrust from the turbine

You're exactly right. But as you suspect, there's reasons why you wouldn't want to do that in all cases. Turbojets derive all of their thrust from the turbine exhaust. It's a small, compact engine, which means high power-to-weight ratio, and it's great for small jet fighters. Unfortunately, it also consumes a lot of fuel. Turboprops are at the other end, where the turbine drives the propeller at much faster speeds than a regular 4-stroke engine would. But the exhaust provides next to no thrust. Turbofans sit in the middle. They provided much better fuel efficiency than a turbojet but greater power than a turbofan. It was very much a "we need a middle solution" type of engine. As turbines became more efficient and compact, the turbofan became smaller as well. To the point that they could be places on a fighter, but with a smaller bypass ratio. This gives much better fuel efficiency (range), while still retaining high power. For jetliners, it's all about efficiency, but still retaining a degree of speed. But for a really high-bypass turbofan (50% or more), it's going to be a huge engine. Fighters are between 15-20% now, but you won't see much more than that. https://en.wikipedia.org/wiki/Bypass_ratio https://en.wikipedia.org/wiki/Bypass_ratio Tom Clancy wrote a book many years ago in which he discusses this in laymans terms really well: http://www.amazon.com/Fighter-Wing-Clancys-Military-Reference/dp/0425217027 http://www.amazon.com/Fighter-Wing-Clancys-Military-Referenc...