Nous commanderons l'horizontal.
Nous commanderons la verticale.


What does it mean?

It means either

We shall command the horizontal.
We shall command the vertical.

or

We shall order the horizontal one.
We shall order the vertical one.

The meaning depends on the context.

Thank you dplax!

Any chance it's an idiomatic expression? Something like going to sleep (nous commanderons l'horizontale, or we'll take the horizontal position, aka lying down in bed) and getting up (... la vertical, or standing up)?

Greatly depends on the context where it's used, and someone with a wee bit more familiarity than I (Luvian?) could clarify whether it is an idiomatic expression, or just an idiotic expression from me :D

I've never heard that phrase before, and I think the first means something a bit rude, to the effect of "the horizontal tango" if you catch my drift.

That sounds like the ad line to "The Outer Limits", an old sci-fi show.

Yup, the Outer Limits. Twas a great show. :D