This is a no-holds-barred artillery unit. This kind of gun started gaining popularity in the 17th century and it grew from there as technology allowed more and more reliable guns to be built. This is one of the more reliable designs of gun from the time period it's iconic name marks how popular it became. These heavy artillery are not easy to move but are technically within the wheeled mobility type Each gun requires a 3 man crew to move, aim and fire the thing. It's special ability is Diagonal Fire, something hard calculate much less counter in the early Renaissance.
Base Social Class
Howitzers are valuable and delicate machines that require relatively small crews to man. This makes them ideal for Peer artillery units. Each Howitzer takes 3 peers from the local population. They will still require housing and Happiness allotment but will also be manning a gun in someone's Garrison or personal army. As peers, they prefer to be hired and paid in Gold Florins whenever the issue comes up.
Base Character Class
While many of the unit types vary in their base class, guns don't have the leisure to specialize in anything but causing lots of damage. Because of this, they (and their Crew) end up resembling the Soldier heroes and level as such. Their attributes focus mainly on Might, Celerity and Toughness and nothing they can equip can't be equipped by Soldiers eventually.
Howitzers are heavy, specialized machines. In order to build a new one, Recruitment buildings need a lot of metal, and in various forms. Each new Howitzer requires not only Iron Ingots and Steel Ingots but also Copper Ore in order to create combat-resistant alloys. During the recruitment/training phase, the Peer crew is trained to shoot at the special angles required by these awesome pieces of artillery.
Obviously you can't put armor coats on a gun, but there are ways to equip your Howitzers and their crew. Each gun can be equipped with one of the bullet types. Their crew can be given Studded leather armor and Manuals. Perhaps best of all, each Howitzer can be equipped with a Horse to help the crew move it from strategic position to strategic position on the battle field.