Reg, G4FGQ wrote:
"A few years back I opened the highish-level kitchen microwave oven door
and felt what seemed to be a warm breeze of air on my face and
especially around my eyes."

I coincidentally happened across a couple of related stories. First,
Louis N.Ridenour wrote in "Radar System Engineering":
"A British Technical Mission arrived in Washington in September 1940 and
mutual disclosures were made of British and American accomplishments in
radar up to that time." Seems the British had invented a magnetron.
America thought it important. On board my ship during WW-2, we kept the
spare for our Raytheon SO radar in the ship`s safe!

Second is from IEEE`s June 2003 edition of "The Institute":
"In 1946, Percy Spencer, an engineer and inventor who held more than 120
patents, was conducting radar-related research for Raytheon Corp. While
testing a new type of vacuum tube - the magnetron - he noticed that the
chocolate bar he had been carrying in his pocket had melted. Intrigued,
Spencer began conducting more experiments. He watched popcorn "pop" and
bounce around the room when he held a bag of uncooked kernals up to the
tube. Next, Spencer observed a raw egg placed next to the magnetron
explode from the pressiure that had built up inside.

Spencer concluded that each of the items had "cooked" when exposed to
low density microwave energy emitted by the magnetron. Raytheon
engineers quickly adapted his discovery, and the first commercial
microwave oven, the "Radarange" began to move into household kutchens
the following year.

Best regards, Richard Harrison, KB5WZI