Whenever I've read about the Louisiana Purchase, the actual mechanics of the purchase is never discussed. For example, the Wikipedia article about it currently states that the US "shipped the gold to France" as if that was as simple a matter as heading down to your local UPS Store.
How exactly was this accomplished, specifically when things like a $3m lump sum down payment gets mentioned? It seems quite risky security wise for a young nation to transport that amount of gold to a ship, then trust the ship to transport it across the ocean, and then transport it from the ship to the French government, not to mention the risk of the ship sinking or getting lost at sea. It seems like the mechanics of this would be quite interesting and potentially have interesting stories around it, but anything I can find just attaches a handwavy footnote at best.
This question could apply to pretty much any historical event before the era of modern technology where a large sum was paid by one entity to some other entity far off, but the Louisiana Purchase was what specifically triggered this question.
There's a least a little of your concern addressed in this earlier answer by /u/stravadarius, mainly that the gold ("almost 10,000 lbs") came earlier with the delegation with the expectation of making a purchase, but more can definitely be said about the ship itself and any security arrangements.
https://www.reddit.com/r/AskHistorians/comments/1df8hl/literally_how_did_the_us_pay_france_the_15m_for/ From user u/bolanrox
The link answers the question more fully and with citations. But to summarize it a bit.
Not sure about the $3 million down payment as the source agrees that might have been gold shipped, but the rest was financed just like you would do it today. The US issued bonds to a bank who then paid out cash to France. The source even has some of the financial terms they agreed too.
The thing I found most interesting is that a British bank (Francis baring and company) facilitated the trade. Considering napoleon wanted/needed the money for his war effort, shocked the British government allowed this to happen. Apparently, the bank didn't tell the government till after the deal was made. In the end, British government decided they would rather France have the money than the land so retroactively gave its approval.
To finance the deal, Barings and Hopes would acquire the $11,250,000 of 6 percent U.S. bonds and pay 52 million francs (in specie) to the French treasury. Barings and Hopes, with help from William Bingham, had just bought Louisiana from France and sold it back to the United States. Almost as an afterthought Francis Baring told British prime minister Henry Addington of the deal they had just financed. On balance the British government's view was that it was better for Britain for Napoleon to have 11 million dollars than for him to retain Louisiana, and gave Baring the (retrospective) go-ahead. By the time Baring and Hopes started making payments France and Britain were already at war again. (Tearle, Barings Bank, William Bingham and the Rise of the American Nation, p. 160).
Edit: added username