I’ll leave it to SteelJaw to tell the story of the birth of Airborne Early Warning, but I did want to touch on one of the key components of his history of Project Cadillac.
Right from the beginning, the folks at MIT’s Radiation Laboratory, in conjunction with Hazeltine, came up with the radar they wanted for airborne early warning, the AN/APS-20. The challenge they faced was more a matter of integrating the radar not with the airplane, but with the fleet.
The radar itself turned out to be remarkably long lived.
Picture stolen from SteelJaw. AN/APS-20 installation on AD-3W.
While it took a highly trained operator to get the most out of the APS-20, it was reliable, and not only worked reasonably well in the AEW role, it was also, when used at low altitudes, a very capable surface search radar.
And because it worked so well, it was fitted to a very wide variety of aircraft. Just off the top of my head:
1. TBM-3W Avenger
2. PB-1W Flying Fortress (Navy version of the B-17)
3. AD-3W, AD-4W, and AD-5W Skyraiders
4. Modified B-29s (oddly, the three modified Air Force B-29s seem to not have had a special variant designation)
5. Grumman AF-2W Guardian (one half of the Guardian Hunter/Killer team, the other half being the AF-2S)
6. WV-2/EC-121 Warning Star (modified Lockheed Constellations)
7. P-2 Neptune family of maritime patrol aircraft
8. HR2S-1W (CH-37 series helicopter modified- two built for testing)
9. ZP-2W Blimps
10. Canadian CP-104 Argus maritime patrol plane
11. Fairey Gannet AEW.3 (modified ASW plane to replace Royal Navy AD-4Ws- they simply pulled the radar sets from the old AD’s, and installed them in new airframes)
When the Royal Navy retired their big deck carriers in 1978, they also retired their Fairey Gannets. But Great Britain still had a desperate need for AEW. The RAF’s project to build their own AEW system was something of a disaster. As an interim solution, they pulled the APS-20 radars from the Royal Navy’s Gannets, and installed them in obsolete Shackelton maritime patrol planes. Up until 1991 the Royal Air Force flew a piston engine powered evolution of the Avro Lancaster equipped with the same radar that had first flow during World War II. As front line equipment.
Not bad for a radar developed as a crash program during wartime.