QuietusEmissary

Checking the Combat Occupations category on Wikipedia turns up:
Peltast: Ancient Greek javelin- and shield-wielding skirmishers. Seems a little obscure, though.
Pioneer (Military): Basically a sapper. Seems like kind of a cop-out for P but it's an option.
Powder Monkey: Carried gunpowder from a supply to cannons, usually on a ship. Might be too late-era for this.
Privateer: This one seems like it could work really well. Although historically anachronistic in fantasy-era settings, generic pirates do get used a lot, so government-backed pirates should be fine.
Several types of pilots and paratroopers: I'm just going to assume that's a "no".
 
And then while looking over all of that to post I realized that PIRATE begins with P. Of course! So that's definitely something.
 
Also Powder Monkey reminded me of the more general Porter, who in a military setting carries gear for other soldiers. A "profession of arms" in a very literal sense. A couple of literal senses, actually.
 
And that's all I got.

PS: Officer
Requires Tactics (for knowing what to do with the troops under his or her command), Oratory (for actually getting them to do it via heroically motivational speeches or the like), and a PS matching the soldiers to be led (so the Officer actually knows how to manage the particular soldiers). Persuasion would be good to pick up as well. PS: Officer represents the training and/or experience required to lead in combat. A successful roll should allow the Officer to gauge the morale of his or her soldiers, get a pretty good idea of the stats and abilities of a Unit (assuming the Mass Combat rules from Fantasy HERO are in use), identify military markings and colors, and coordinate his or her Unit with others in the same army.
 
Example of PS: Officer in use:
An Elf Marshal is leading a Unit of Elf Soldiers into battle. They charge toward a mass of goblins, and the Marshal makes a PS: Officer Roll to identify them, even from pretty far out, as Goblin Archers. He orders his troops to form a phalanx, and they are amply prepared for the barrage of arrows that rains down on them.
A brigade of goblins on wargs (because what else would goblins ride?) charge into the elves' army, and the Marshal's Unit begins to take casualties. Even before the Unit loses Readiness (Fantasy HERO p. 235), a PS: Officer Roll tells our hero that things are not going well and the morale of his soldiers is beginning to break. He charges into the fray with renewed vigor, cleaving a warg's head from its body before delivering an inspirational war cry, improving the Unit's Morale Roll as described on page 236 of Fantasy HERO.
The goblins' numbers begin to overwhelm the elven army, and the Units that comprise it begin to disengage one by one. The Marshal's Unit has withdrawn a bit due to casualties, but a PS: Officer Roll will allow them to successfully cover their allies' retreat with minimal risk to themselves.
 
Officer Template:
On a related note, when I am building an NPC to command a Unit or a group of other NPCs, I usually start by taking a normal member of that Unit or one of those combat NPCs and adding +1 to OCV and DCV (to represent combat experience and advanced training), as well as the Skills listed in the PS: Officer description and the Fringe Benefit: Military Rank Perk. I also often add an ability like the following:
 
Combat Leadership
Effects: Aid 2d6 (STR, PRE), Boost, SER (5), Expanded Effect (2 Elements; +1/2), AOE (16m Radius, Selective; +1) (30 Active Points); Requires a Tactics Skill Roll (-1/2), Only Aid Others (-1/2), Incantations (Throughout; -1/2), No Range (-1/2), Limited Power (Increased Characteristics only apply to combat effects, such as adding damage to a melee Attack or resisting Presence Attacks; -1/2)
Description: As long as the Officer is alive and within earshot of his troops, he can motivate them--whether through admiration, loyalty, or fear--to great feats of martial prowess. Different Characteristics can be added or substituted for the ones listed above. Examples include CON ("We can rest when we've cleansed this land of our foes!"), OCV ("Strike true!"), STUN ("Grit your teeth and push forward!"), or BODY ("No matter the cost, we will fight to the end!"). To simulate non-combat leadership abilities, such as the harsh commands of a slave-driver, change the Limited Power to only work outside of combat (in which case I would say it's worth -1 instead of -1/2) or remove it entirely.
Power Cost: 8