
When life gives you lemons, make advanced aircraft alloys
Context: Magnesium-Elektron Ltd (today Luxfer MEL Technologies) was a British magnesium alloys manufacturer founded in the 1930s, partly owned by and using the products and processes of IG Farben, the German chemicals giant which at one point was the largest conglomerate in Europe and the world's biggest chemicals manufacturer.
At this time magnesium manufacturing used ores and minerals from salt lakes and solution mining, as well as from rocks such as dolomite and magnesite. Magnesium as a metal is super reactive so it can't be extracted by heating like with iron. You first need to produce magnesium chloride, which then needs to be electrolysed to make the pure metal. IG Farben's process was to grab magnesium oxide (for example from crushed and calcinated ores) and then blast it in a 1000°C furnace while pumping in chlorine gas (called the Chlorinator), which was then scooped out as a molten soup and electroplated, recycling the gas. After all this was done you got magnesium metal, pretty strong and very light, perfect for aircraft. Most of the industrial developments had come from Germany, and by 1938 nazi Germany was making more magnesium than every other country combined.
Anyway in 1939 the UK declares war on nazi Germany, and within weeks German subs are already sinking ships around Britain. MEL was in a bind, as they no longer had reliable supplies from abroad, were cut off from IG Farben, were in a country actively fighting the company whose stuff they were using, and British demand for aircraft production was only increasing. The thing is though that magnesium isn't actually that difficult to find, it's the 4th most common element on earth, the 8th most in the crust, and the 3rd most common element dissolved in seawater (after you know, the sodium chloride). The hard part has always been separating it out.
Enter the Dow process, pioneered by Dow Chemical in the US, who worked out that mixing calcium oxide and seawater allowed insoluble magnesium hydroxide sludge to be separated, which after the addition of hydrochloric acid, produced your electrolysis precursor. In this way, by 1941 MEL could produce magnesium metal by pulling it right out of the sea from the comfort of wartime Britain (well, Hartlepool and Manchester), making thousands of tons across the war for all sorts of industries. Nowadays magnesium is the third most common structural metal, used for everything from car parts and pyrotechnics to temporary prosthetics and laxatives.
TL;DR during WWII a British magnesium manufacturer was cut off from their supply, but got around it by yoinking metal straight out of the ocean and using it to build planes