Not napalm. Here's another clue. Good to see all this participation!
Looking for a piece of equipment carried on a number of combat aircraft.
1. It was somewhat low tech, at least conceptually. More like Miss Tilly's diaphragm than the cavity magnetron.
2. Two distinct varieties were produced.
3. It was needed because of a shortcoming of a much-more-sophisticated item of equipment used by aircraft doing a particular job.
4. It was developed by an officer whose day job was not technical and did not require him to fly, although he had been a pilot in an earlier war.
5. It was so effective that it forced the enemy to change their tactics.
6. The officer who thought of it got the idea from conversations he had with aircrews who complained about the shortcomings of their equipment.