“What would have been the effect on the early post war designs if a turbofan had been available in the late 40’s?” Not much; no role.

Start in 1944. If its rapid climb you want, then turbojet. For endurance, Big recip – Eagle/Pennine. We’re trying the propellor-turbine, though bothered about its sfc; we’re funding Clyde/Dart/Tweed at RR, Proteus/Theseus at Bristol, Mamba/Python at MetroVick. Power Jets is trying W2/700, plenum-chamber-burning turbofan, Miles M.52 as FTB.

Move to 1947. W2/700 and M.52 lapsed in 1946 as we had neither enemy nor money. RR, trying too much, is making a mess of AJ.65 axial turbojet. Bristol starts B.E.10 (to be Olympus 100), MoS moves F.9 from MetroVick to ASM, to be Sapphire: these turbojets are chosen for Avro/HP Mediums because we need all-the-power-we-can get to lift the ghastly bulk of Blue Danube high to Moscow. Halford, trying too much at DH, sees EE sell his Napier E.113 turbofan scheme to RR: it had been chosen for Short Sperrin, but Hives substitutes AJ.65 and dams various Clydes so he can attend to fixing (to be Avon) and placing it on Geo.Edwards’ proper Medium.

1950: RR places (E.113, now)RB.80 Conway on Valiant B.2 (Avon, prot.only): it’s a low pathfinder – endurance (=turbofan) more than power (=turbojet). But it gets chopped. Mid-1950s: floods of Avons, Olympii, Sapphires, berthed where power beats endurance.

Conway was revived for Victor 2 because its Bomb was to be lighter, its range greater, so well-met by BPR >1. Range (or lower fuel burn) became a civil attribute, admitting Conway and JT3D-3B to displace JT4A. Modest BPR had no especial virtue: it’s the big fan that makes turbofans worthwhile, and that needed the metallurgical innovations of 1963.