I'm aware of methamphetamine's history in WWII, but there it was being produced on an industrial scale, with presumably fewer jerry-rigged components. Wikipedia also informs me that methamphetamine use in America became more popular in the 1980s, but based on the statement that the drug was coming from manufacturers in Mexico, I assume that it was also being produced on a more industrial scale.
I was wondering when improvised synthesis of methamphetamine became more widespread. More specifically, I'm wondering when the whole "guy in a trailer using road flares for red phosphorus" style of production surfaced in America. It seems kinda odd to me that knowledge of a series of reactions that would require a fairly in-depth knowledge of chemistry would make its way into areas of the country that are pretty impoverished.
The "improvised synthesis of methamphetamine" first crops up in the US during the 60s and 70s though it's history is older.
Meth in that period was prevalent in the west coast of the US and mostly the purview of outlaw biker gangs who were linked to other aspects of the drug trade. They used the "California Cook" or P2P method. These were the first "clan labs" associated with meth production in the US and they were very dangerous. The production quality of the P2P method is also pretty inefficient and the resulting meth is usually of lower grade than other methods.
In the 80s and 90s, the "Nazi Cold Cook" method took off, and it used anhydrous ammonia and ephedrine, mainly acquired through theft of farm supplies and large scale purchases of over the counter ephedrine and pseudoephedrine.
That became the predominant "clan lab" in the US, into the early 2000s. It started to lose popularity as the DEA and states tightened the sale of ephedrine/Sudofed and fertilizer suppliers and users made it harder to steal or acquire anhydrous ammonia. The early 2000s also saw a major shift in meth supplies from internal to the US to Mexico as "home cookers" ceased to be the main source for meth in the black drugs market. It was more efficient and cheaper to smuggle industrial scale produced meth across the border. In a way, the enforcement activities that successfully reduced the number of clan labs in the US, led to a "professionalization" and "commoditization" of the meth market.
The alternate form of production is the "red P" method you refer to (of which there are two primary variations). This has been around for a while and popped up in clan labs from time to time but was not as popular as the Cold Cook among home brewets. It is the primary production method used in Mexican labs, however.
Source: Long ago, in a land far away, I attended an abbreviated version of the DEA Clan Lab course and worked with a number of meth task forces, but since that might be seen as "anecdotal" by the ever vigilant Moderators, I recommend you see this DOJ publication for a start: https://www.justice.gov/archive/ndic/pubs13/13853/product.htm