What Is? The Nerathan Bireme

What is the most popular military vessel in your world? Where was it made and how does it work?
By far, the most popular military vessel in the Reach is the Nerathan Ironwood Bireme. These large, fast, heavy and, most importantly, expensive warships are only made by the Nerathan Empire, who once dominated the Iron Sea. However, they are not exclusively used by the Nerathans. During times of economic uncertainty, the shipwrights of Nerath would build for whoever had the coin. While most Nerathan Biremes are built to a common hull plan, each ship's armament and sail rigging differ depending on the ship's owner and purpose. Nerathan Navy Siege Biremes are equipped with siege bombards on rotating mounts, or with similar trebuechets when bombards couldn't be sourced, while the Wicked Wench, one of the only Nerathan Biremes owned by a private person, is equipped with a broadside of ballistae and a mangonel each on the fore and aft.
The oldest of these ships was built around 800 IY and only 153 of these Biremes were put to sea before Ironwood sourcing issues ended their production in 1177 IY (~101 years ago). Of the 153, sixty-three are known as sunk, thirty-nine equip the Nerathan Imperial Navy, ten are owned by the Silver Empire of Avathon, one owned personally by the Silver Empress herself, two each are owned by Thanes of Khayern and Angdar, one owned by the Steel Banner mercenary company of Trost, another four privately owned, finally, seventeen are dispersed to various trading houses that rule the cities of the Mirar Sea; all other examples are considered lost. A typical Nerathan Ironwood Bireme costs 250,000gp, requires 215 crew to sail at full efficiency of which only fifteen must be skilled sailors (the rest are unskilled rowers), and cannot be crafted.