A couple of unrelated to military history ones I had a hand in were:

Growing SiAlON (Silicon Aluminum Oxygen Nitrogen) whisker reinforcements for advanced ceramics. I worked at a company that gave me a sketch design for a furnace to grow Silicon Carbide powder in a continious production process. I built a working prototype from the sketch.
As a side result that was completely unintended, it made the longest (at least 8"+ perfect SiAlON whiskers ever produced! Better than Sandia Labs did in a special reactor for just that purpose and at a fraction of the cost. It also made OK SiC.
The other was making a reactor for Carbon 60. Made the first one from basically junk lying around the building. Power supply was an arc welder on sale at Sears....really... Best part I saw that POS on a NOVA episode on Carbon 60 and one the lab techs later made by scaling up my design and using eight (8!) of the same arc welders! I was ROFLMAO seeing that!