French Letters and condoms

Question

Repartee (inexact quote) from a TV show:

Person A: Now, we're going to be getting some letters from French people.
Person B: It could be worse. You might be getting French letters.
(laughter)

Going by ODO and Webster, French letter appears to be a BrE euphemism for a condom. How did this come about?

Answer 1

OED provides no help, only an early citation:

French letter n. colloq. = condom n.
?1844 Exquisite in P. Fryer Man of Pleasure's Companion 131 Gentlemen who live in London will be at no loss in easily obtaining these ‘French Letters’.

Etymonline gives some help and a plausible explanation:

French letter "condom" (c.1856), French (v.) "perform oral sex on" (c.1917) and French kiss (1923) all probably stem from the Anglo-Saxon equation of Gallic culture and sexual sophistication, a sense first recorded 1749 in French novel.

I suspect that it's called a letter because of its packaging at the time, but I don't know how to verify that.

Answer 2

I was sure this was a duplicate, but can't find it.

Many countries with longstanding rivalries use each other's names to mean "fake". For example, in the UK:

• French windows are actually doors (called French doors in the US)
• French leave is going awol (in France they say filer a l'anglaise for the same thing)
• French letters are condoms

While in the US:

• Dutch courage is being drunk
• a Dutch treat is neither treating the other
• a Dutch uncle is not your uncle
• a Dutch oven is not an oven (it's a heavy lidded pot you can achieve baking-like results with on the stovetop)

and so on

As far as I can tell, in the US, French typically means "cut into long thin strips" (French fries, frenched beans, frenched ribs on a roast) or "the glamourous luurious way they do it in France" - French vanilla, French bread. In some parts of the country it once seems to have meant racy or sexy - the French postcards in Oklahoma! for example. I think French kiss falls into that category.

Answer 3

Would it be possible that "letter" here were a derivation of the verb "let" in the archaic meaning given in the OED:

1. trans. To hinder, prevent, obstruct, stand in the way of (a person, thing, action, etc.).

A "French letter" could then be a "French" device (French because in the olden times anything wicked would come from the French) that would prevent diseases/pregnancies, etc..