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Massachusetts Institute of Technology had set up a secret laboratory;

Yeah, a "temporary" building, #17, that they didn't tear down until about 2000. It also housed the office of that anti-American linguist, whose name escapes me at the moment.

by November, the cavity magnetron was in mass production;

One of the problems they had was the ability to duplicate the original prototype at first. Samples didn't perform like the original, and that was not a good thing. A complete technical analysis was required of each part and step of the manufacturing process. I can't remember exactly what was found that threw off the end product.

Some of the most significant leaps of technology have been truly accidental, as described in the following excerpt from

Cavity Magnetron

Randall and Boot were assigned to research and develop radar receivers, while another team, in a distant city, were tasked to research and develop radar transmitters.

Every very rare now and then people who are newcomers to a field make a great discovery, simply because they don't know what works and what doesn't.

Randall and Boot didn't know much about generating microwaves, so they set about learning how. There were two devices available at the time for the task. The first was the "magnetron", which was basically a classic vacuum diode with a magnetic field placed across it. The interaction between the external magnetic field and the electron flow through the tube produced microwaves. The other was the "klystron", much more recently invented by the brothers Sigurd and Russell Varian at Stanford University in California, and based on a "resonant cavity" through which streams of electrons flowed. Oliphant's team believed the klystron was the solution for short-wavelength radar.

Randall and Boot didn't want to spend a lot of time and effort generating microwaves for test purposes. They focused on the less sophisticated magnetron simply because it seemed simpler to work with. As they learned about the magnetron, however, they realized that they could combine features of the magnetron and the klystron and come up with something new.

Working on a shoestring budget, the two men pieced together their new "cavity magnetron", as they called it. The core of the cavity magnetron was a thick copper cylinder, with a large central tunnel bored through it. Six smaller tunnels, or "resonant cavities", were bored around the central tunnel, and connected to the central tunnel through slots running down their length.

The copper cylinder was positively charged, forming the "anode" of the tube. A metal conduit was inserted down the central tunnel. The conduit was negatively charged, forming the "cathode" of the tube. The cylinder assembly was sealed at the ends, and a magnetic field placed across it. Under the combined influence of the electrical potential between anode and cathode and the magnetic field, electrons circulated in the central tunnel, producing electromagnetic radiation in the resonant cavities. The electromagnetic radiation from the cavities coupled together in the central tunnel, interacting with the electron flow to efficiently extract energy from it with high efficiency.