According to a playwright, a certain famous face "launched a thousand ships." What amount of beauty, in a subsequent reckoning, would be required to get just one ship underway? And who can give me the proper citation for that "ships" quotation?

Inspired by the line "Was this the face that launched a thousand ships...?" from Marlowe's play The Tragical History of Doctor Faustus, it was determined that a Millihelen is the amount of beauty that can launch one ship.

https://en.wikipedia.org/wiki/Helen_of_troy

Here is the entire passage:
Faustus includes a well-known speech addressed to the summoned shade of Helen of Troy, in Act V, scene i. The following text is from the Gutenberg project e-text of the 1616 quarto (with footnotes removed).

FAUSTUS. Was this the face that launch'd a thousand ships,
And burnt the topless towers of Ilium?--
Sweet Helen, make me immortal with a kiss.--
[Kisses her.]
Her lips suck forth my soul: see, where it flies!--
Come, Helen, come, give me my soul again.
Here will I dwell, for heaven is in these lips,
And all is dross that is not Helena.
I will be Paris, and for love of thee,
Instead of Troy, shall Wittenberg be sack'd;
And I will combat with weak Menelaus,
And wear thy colours on my plumed crest;
Yea, I will wound Achilles in the heel,
And then return to Helen for a kiss.
O, thou art fairer than the evening air
Clad in the beauty of a thousand stars;
Brighter art thou than flaming Jupiter
When he appear'd to hapless Semele;
More lovely than the monarch of the sky
In wanton Arethusa's azur'd arms;
And none but thou shalt be my paramour!

https://en.wikipedia.org/wiki/The_Tragical_History_of_Doctor_Faustus

OK, perhaps I'm misunderstanding here, but I THINK what you wanted (among other things) was the reasoning behind the quote? If not, please ignore, if so, read on:

When Helen of Troy was betrothed to Meneleaus, her beauty was so that in order to keep other suitors (and she had many) from her door the king (Menealus) secured from all the other nobles the promise of support should he need it. In other words, treaties were signed, and such treaties would rule out an attempt at wooing or even kidnapping Helen.
So when Paris, prince of Troy, eloped with her, Menealus, Agamenon and all the other nobles and kings who had aigned the agreement launched their ships towards Troy in order to destroy the city and take Helen back.
Thus Helen's face was, indeed, that which launched a thousand ships. (It probably wasn't literally a thousand -- it could have been more, or less, but somehow, "the face that launched eight-hundred-and ninety-four ships" just doesn't have the same ring to it!)
Hope that helps!
Troll