Particle physics laboratory

Remembering the MIT Radiation Lab

In the late 1980s, our company managed to procure the complete 28-volume MIT Radiation Laboratory (Rad Lab) series, published in 1947, for the company’s library. For me, these books were interesting because I love history and ancient technology, but I couldn’t understand why everyone was so excited about the acquisition. Only a cursory glance at the volumes would reveal that the “circuits” described in these books used vacuum tubes and their “computers” consisted of mechanical linkages. It was the 1980s and we were working with modern radar and communication systems using semiconductors, integrated circuits and digital computers. How could those moldy old books be of any practical use? To my surprise, it turned out that indeed they could, and I ended up enjoying the excitement. I’ve even used several myself over the years.

Radiation lab? Nuclear radar?

In the years before World War II, the idea of ​​a civilian organization of scientists that would operate independently of military and government bureaucracies was championed by Dr. Vannevar Bush. The military and science had not worked well together during World War I, and it seemed science and technology would play a much greater role in the future.

It seemed certain that America would eventually enter the conflict, and Dr. Bush and others believed that a new organizational framework was needed. To this end, the National Defense Research Committee (NDRC), which later became the Office of Scientific Research and Development (OSRD), was presented to President Roosevelt and he approved it in June 1940.

Almost immediately, a gift fell into the lap of the new organization – the Tizard Mission which arrived in the United Kingdom States in September 1940. They brought a veritable treasure chest of technical innovations from the British, who hoped that the cooperation of American industry could help them survive what looked like a certain and imminent invasion. One of those treasures was the cavity magnetron, which our own Dan Maloney wrote about a few years ago.

Within weeks, under the guidance of young Welshman “Taffy” Bowen, they had reviewed the design and assembled the equipment needed to get it up and running. A 10 kV anode feed and 1,500 gauss electromagnet were purchased, and the scientists gathered at Bell Radio Laboratories in Whippany New Jersey on Sunday, October 6, 1940. They powered the cavity magnetron and were blown away by the results – over 10kW of 3GHz RF (10cm) from something the size of a bar of soap.

A flurry of activity ensued, and the Radiation Laboratory was officially established on October 25, located at MIT and operating under the aegis of the NDRC. The name was going to be Microwave Laboratory, but it was changed to Radiation Laboratory instead to mislead prying eyes as to what they were researching. At that time, radiation research laboratories, such as Nobel laureate Ernest Lawrence’s Berkeley Radiation Laboratory, had a purely scientific scope unimportant in wartime.

The Push to Reduce Wavelengths

Why all this fuss? Although radar systems were little used at that time, they all operated in the VHF band. Engineers at the time knew the VHF frequency band and therefore had the design tools and components needed to build working units. By the late 1930s the British had built an extensive range of coastal defense radar stations called Chain Home, whose operation overlapped HF and VHF. Since the start of the war in September 1939, certain weaknesses in the system had become apparent. The 200 MHz Chain Home Low system addressed some of these concerns, but the shorter wavelengths of centimeter radar (in the SHF region) promised real benefits. For example, antennas could be smaller, smaller objects could be detected and located with better accuracy. But there was no way to generate the necessary transmit power until the introduction of the cavity magnetron.

Along with the cavity magnetron itself, the British presented their American counterparts with a list of priorities. They immediately needed three types of radar: (1) air intercept, (2) anti-aircraft fire direction, and (3) long-range bomber navigation. The Rad Lab agreed and immediately launched three corresponding crash programs.

Project 1: Airborne Interception Radar

B-18 used as a flying radar laboratory

Within three months, the team had their prototype 10cm airborne radar up and running. Built in true hacker style, it filled an entire roof and was cobbled together with anything they could get their hands on. By early January they had a working system with two antennas, and by February they had solved the transmit-receive switch problem and demonstrated successful aircraft tracking using only “one eye”. By March, they had scaled down the sprawling prototype to something that could be fitted into an airplane. On its first test flight, the crew demonstrated air-to-air detection and, on a whim, tried and succeeded in detecting ships and submarines.

Project 2: Anti-Aircraft Gun Radar

This project was in full swing at the beginning of 1941. The original ideas presented by the British, in fact the operation of existing VHF systems, were completely manual. The radar would find the planes, but people pointed the antennae and fired the cannons – basically a really improved searchlight. But Rad Lab scientists thought they could do better by automating the whole process. They proved the naysayers wrong, and in May 1941 a radar was working that could automatically track planes and point a camera at the plane. Bell Labs developed an analog fire control computer, and a working system was completed in April 1942 (SCR-584 radar).

Project 3: Long distance navigation

Loran AN/APN-4 receiver set

Development of the Long Range Navigation, or LORAN, project began right away. The first pair of stations was under construction in the spring. LORAN was the only Rad Lab project not to use microwaves. Instead, it operated around 2 MHz and was used to guide aircraft and ships. LORAN and its successors continued to be used in the United States until 2010 and in Europe until 2015.

These are just the first three projects. By the end of the war, the Rad Lab had also developed and contributed to many other new radar applications, including new 3 cm and 1 cm systems.

Working environment

The Rad Lab needed staff quickly and began recruiting physicists and engineers from universities across the country. Everyone agreed that it was a great place to work. There was a free exchange of ideas, the excitement of pushing new boundaries in engineering and physics. Decades before modems and BBSs, the Internet, or our own weekly Hackaday chat, Rad Lab staff had weekly teletype conferences with colleagues around the world.

The Laboratory has never adhered to a rigid organization chart, based on a so-called preconceived logic or function; rather, the organization was built around available men. [The policy was to] free scientists from unscientific control. Over the past two years, the Laboratory has begun to be controlled more by non-scientific elements. But that came too late to frustrate important aspects of the program. Lee Alvin DuBridge, Founding Director of Rad Lab

The ever-present urgency of war would always weigh on decisions. Anyone coming up with a new idea would always be challenged by associate director II Rabi with the question: “How many Germans will she kill?”. [Ed Note: Different times!]

Heritage

In addition to the success of the first three projects, the Rad Lab has continued to contribute and expand radar applications. These projects included microwave landing systems, underwater hunting radars, electronic countermeasures and counter-countermeasures, identification friend or foe (IFF), early warning radar and shell rocket radars, among others. At its peak, the Rad Lab employed over 3,000 workers, including several future Nobel laureates, including II Rabi (Physics 1944) and Ed Purcell (Physics, 1952) for discoveries involving nuclear magnetic resonance.

Excerpt from Building Approval Letter 20

One of the temporary structures built to house the sprawling laboratory in 1943 was simply called Building 20 and became a legend in itself for decades. Being of temporary construction, people did not bother to drill holes in the walls to run the cables. It is said that 20% of all American physicists have worked in Building 20 at one time or another and earned the name “The Magic Incubator”. It was finally demolished in 1998 to make way for a modern university complex.

An encyclopedia of knowledge

After the war ended, the Rad Lab closed on December 31, 1945. A final task was to document the work done during the five years of operation. Deputy Director Louis Ridenour led the task, asking scientists to document their work before returning to normal life. The result was a set of 28 volumes, including the index.

Rad Lab Series Volume 1

During my years of working with radar systems, we have regularly used some of these books. It wouldn’t be uncommon to hear someone screaming in the hallway, “Who stole Silver from my desk last night?” » — Samuel Silver was the author of the Antenna Book, Volume 12. I used Marcuvitz’s Waveguide Handbook, Volume 10 quite a bit. And when he was assigned to a project using time-of-flight calculations, I learned a lot from the LORAN book.

In the 2020s, are some of these volumes still significant? I would say that the theoretical texts are still valid, but there are probably plenty of other texts, more modern, more easily accessible. For retro circuit enthusiasts, these books contain many examples of vacuum tube designs to learn. And if you like mechanical computers, the book on mechanics and computer links might interest you. This series is long out of print, but is available on the Internet Archive (link to Volume 1).

Banner image courtesy of MIT Museum.