This is a case where punctuation might help. I'd recommend a dash:

Small Units – Each with a Clear Mission.

Dashes are used “to set off a word or phrase after an independent clause.” In this case, the dash offers a concise way to emphasize that each unit has a clear mission, while preventing the title from becoming overly wordy.

In think the inclusion of the word each would solve your problem. NOAD says in its definition for each:

each (adj. & pronoun) used to refer to every one of two or more people or things, regarded and identified separately

So, you could simply give your presentation this title:

Small Units – Each with a Clear Mission

As an aside, I prefer using a dash in the title. Dashes are used “to set off a word or phrase after an independent clause.” In this case, the dash offers a concise way to emphasize that each unit has a clear mission, while preventing the title from becoming overly wordy. You could used a colon, too (except colons are sometimes used to indicate a subtitle of a book, so that might make "Each with a Clear Mission" look more like a subtitle, as opposed to part of the title). A comma could work, also:

Small Units, Each with a Clear Mission

but I prefer the dash. Still, that’s a matter of preference.