Project Cadillac: How the U.S. Navy Invented the Flying Radar Station
What is that strange-looking aircraft, that looks like an airliner with a giant mushroom perched on top? From that giant mushroom perched high up in the sky, perhaps over Iraq or Syria or the South China Sea, invisible beams of radiation stream in all directions.
Be it America's AWACS, Russia's A-50 or China's KJ-2000, flying radar stations have become a fact of life in modern warfare. From their high-altitude vantage point, Airborne Early Warning & Control, or AEW&C, aircraft can peer into places that ground-based radars can't. Utilizing their radar data, they can function as aerial command posts to manage an air battle with a speed and efficiency that 1918 or 1945 air commanders could only dream of.
But the flying radar station actually dates back to World War II, the first conflict to feature ground-based radar guiding fighters to intercept enemy bombers conducting daytime raids. But to detect night bombers cloaked by darkness, radar was soon installed on night fighters, usually twin-engined heavy fighters or converted bombers sprouting insect-like antennae from their noses. Yet these were short-range devices designed to enable an interceptor to detect, stalk and then maneuver into firing position to shoot down a bomber.
However, in February 1944, the U.S. Navy had a thought: instead of a short-range combat radar, how about a more powerful device that could perform long-range search? Thus was born Project Cadillac.
Project Cadillac (named after the Maine mountain that is the highest on the East Coast) was an “ambitious program to develop an AEW system that would be deployed with the fast carrier forces in the Pacific,” according to a series of articles published by the U.S. Naval Institute. “It was envisioned that the system would be in place for Operation Downfall, the projected invasion of the Japanese homeland, slated for sometime in early 1946.”
“As originally envisioned, Cadillac would consist of two sections: one airborne (“AEW Aircraft”) and the other shipboard (“CV CIC”). The airborne unit would carry the APS-20 radar, IFF and VHF comms and relay equipment, acting as an airborne radar and relay platform for the ship. Back on the ship, the radar picture from the airborne unit would be relayed via a VHF video data link and displayed on a dedicated PPI (Plan Position Indicator) scope. Communications with far-flung fighter CAP would also be relayed through the airborne unit. Sorting out friend from foe would be via the newly developed IFF or Identification Friend Foe system which relied on an aircraft responding to electronic 'challenge' signals with a coded pulse train. The airborne unit would also have the ability to display its own ship’s radar picture and have a limited capability to control fighters, but this was planned to be a fall-back capability.”
If this sounds like a modern radar aircraft, such as the Navy's E-2 Hawkeye, the resemblance is not coincidental. The difference, though, was that Project Cadillac aircraft would function solely as radar stations, rather than exercise command and control like the AWACS or the Navy's E-2 Hawkeye carrier-based aircraft.
Project Cadillac combined British development of the cavity magnetron -- the same technology that today heats up your dinner in the microwave -- with American development of electronic relays that extended the range of radar beams. The massive effort involved 9 out of the 11 research labs at the Massachusetts Institute of Technology-Radiation Laboratory, as well as the Navy's Naval Research Laboratory, Bureau of Aeronautics and Bureau of Ships.
As it turned out, a flying radar station was exactly what the Navy needed. By the summer of 1945, the Navy was taking a beating from kamikazes, with dozens of ships sunk and hundreds more damaged. Combat Air Patrol fighters and shipboard anti-aircraft guns took a fearsome toll, but suicide aircraft continued to slam into American ships. Most vulnerable during the Battle of Okinawa were the radar picket destroyers, whose lonely vigil as the distant eyes of the fleet rendered them kamikaze bait. Clearly a better solution was needed then sacrificing ships and crews to gain a few precious minutes of early warning.
The AN/APS-20 was the world's first AEW radar. Tests showed the airborne radar could detect aircraft as far as 100 miles away. However, the only carrier-based aircraft large enough to mount the APS-20 radar and its eight-foot antenna was the TBF Avenger torpedo bomber designed by Grumman, or more specifically the TBM model manufactured by General Motors.
The TBM-3W, with its big underbelly bulge housing the radar gear, entered service in March 1945. The Navy ordered about 40 aircraft, though the war ended before they became see combat. The TBM-3W became operational in 1946, though ironically, it was paired with the TBM-3S armed anti-submarine aircraft to hunt subs. The TBM-3W's radar signal would bounce off a sub, and then be picked up by a radar receiver aboard the TBM-3S, which would then swoop in for the kill.
By modern standards, the first flying radar station was not impressive. The APY-9, mounted on the latest E-2D Advanced Hawkeye, can reportedly detect aircraft 350 miles away. Yet today's radar planes are the direct descendants of Project Cadillac.