[RPG] Is it possible to have a character with proficiency in all martial weapons without proficiency in Medium armor

dnd-5emagic-itemsproficiencyweapons

When thinking more about this question: Are the requirements of a Horn of Valhalla cumulative?, I started to wonder if characters could effectively use horns without being able to use their lesser counterparts.

Being able to use Bronze, but not Brass is easily met by druids or many different characters with the Moderately Armored feat. However, I have not found a way to be proficient in all martial weapons without also having proficiency in Medium armor (i.e. to use the Iron horn, but not the Bronze). Is it possible?

I'd like to only include official classes, races, and backgrounds (not including Unearthed Arcana). Feats and multiclassing are acceptable.

Best Answer

Multiclass Barbarian

Any character who is not proficient in medium armor (and has 13 Strength or more) can multiclass (if using that optional rule) into Barbarian to gain proficiency in martial weapons without gaining proficiency in any new armors.

Multiclassing Proficiencies

\begin{array}{|l|lr|} \hline \text{Class} & \text{Proficiencies Gained} & \kern 10em \\ \hline \text{Barbarian} & \text{Shields, simple weapons, martial weapons} \\ \hline \text{...} & \text{...} \\ \hline \end{array}

Multiclassing, Player's Handbook, pg. 164