one of the first / firsts

[hwipster]

Hello,
if i'd like to mention something that was not the first but the 2nd 3rd 4th, so somewhere at the start, shall I say 'one of the firsts' or 'one of the first'? Is 'one of the first' legit in itself without a plural noun following? I saw it in a text and I dunno whether it's a typo or not.

Example:

Fact:
The Millennium Underground was one of the first undergrounds in the world.

Questionned form:

A) The Millennium Underground was one of the first in the world.
B) The Millennium Underground was one of the firsts in the world.

And how does this apply when it is in a slogan-like construction: "Millennium Underground - one of the first(s?) in the world.

Since 'one of' implies plural, my sense really misses the 's', but maybe it is an idiom where such logic doesn't apply.

Thanks in advance for suggestions,

 

[Barque]

The Millennium Underground was one of the first undergrounds in the world.

I'd prefer "one of the first underground railways in the world" but otherwise it's fine.

A) The Millennium Underground was one of the first in the world.

This is possible if you've already made it clear you're referring to underground railways.

B) The Millennium Underground was one of the firsts in the world.

This is wrong.

when it is in a slogan-like construction: "Millennium Underground - one of the first(s?) in the world.

"One of the firsts" is wrong.