Turbojets have a smaller intake and the entire thing produces thrust. Unlike today's much more efficient turbofans, where a small turbojet turns the larger fans to produce most of the thrust.

https://en.wikipedia.org/wiki/Hawker_Siddeley_Nimrod

In the early 2000s, BAe Systems had a project in train to upgrade them to the MRA4 spec, essentially remanufacturing the existing MRA2/MRA3 Nimrods around a new wing structure that could accommodate RR BR700 turbofans, doubling the aircraft's range:

https://en.wikipedia.org/wiki/BAE_Systems_Nimrod_MRA4

(Go look at the photos on the respective wikipedia pages and examine the engine inlets at the wing roots: the MRA4's air intakes are much larger.)

The MRA4 upgrade was at least as radical as the proposal to re-engine USAF B-52 bombers with four GE high-bypass turbofans (as seen in the photograph on the web page below, showing a B-52 flying with the new engine in the inboard starboard pod):

http://aviationweek.com/defense/ge-rolls-pratt-vie-b-52-engi...

... Which also got cancelled; in the case of the B-52 the USAF had so many old engines in mothballs that re-engining the B-52 would cost more than just swapping out old units, and in the case of the Nimrod MRA4 the program ran into nightmarish cost-overruns when it became apparent that the aircraft they were trying to remanufacture were all different — the RAF's Nimrod fleet had been hand-built then patched for half a century and simply couldn't be consistently upgrades.

(Moral of story: upgrading a 50+ year old design is harder than it looks.)

Ah those innocent days, before the QE carriers and the F35 made that look like mere pocket change.

Also they were supposed to be convertible to cats & traps at the drop of a hat, which would have allowed the UK to procure a non-BAe fighter to fly off them, couldn't have that...

They are very cool looking.

http://i.imgur.com/L4KLas2.jpg

https://www.youtube.com/watch?v=a2PBOdTk3vE

https://courses.edx.org/courses/course-v1:DelftX+AE1110x+3T2...