I'd forgotten about this: making ammo right under the nose

of the British Army:
The head of the clandestine Israel Military Industry, Yosef Avidar, devised a plan to smuggle in machines for a secret factory to make the bullets. Though he was successful in purchasing machines in Poland in 1938, the Zionists could only get them as far as Beirut, where they were stored for nearly four years before Jews who served in the British army succeeded in bringing them to Palestine.

The ammunition plant was built almost under the noses of the British, who had a nearby base. The site was a place where pioneers would go for training in kibbutz life before moving on to establish cooperatives around the country. Under the code name "the Ayalon Institute," a group of pioneers from the Hatzofim Aleph movement and members of the Haganah (and, later, joined by members of the Palmach) dug a large underground chamber 300 square yards 13 feet underground with nearly 2-foot-thick walls and ceiling. The entire project was completed in 22 days. To conceal the clandestine project, the Jews built housing, a dining hall, chicken coop, cow barn, workshops, a laundry a bakery, and a vegetable garden to give the outward appearance of an ordinary kibbutz.
22 days. In a time and place where being caught making ammo meant a death sentence.

Thanks to Tuccille for the reminder. And some links to 'make your own gun' plans.