Presumably a contemporary German made the above sketch of Koxinga's Iron-man Corps, one of the many special forces of Koxinga's army. It shows infantrymen who donned a helmet, face mask, heavy chest and arm fish-scale armors, and a long heavily-armored skirt. They each carried a long spear or a broad-blade at the end of a stick - weapons for cutting down enemy cavalries. They were also accompanied by the rattan-shield infantry who erected inch-thick curtains to catch arrows and bullets. According to Chinese accounts, however, both arms and legs of these iron-men were exposed - for easier movement. And they went bare-footed for more steady footing. The Qing strategy of targeting their feet with arrows failed because the Iron-men would simply pluck out the arrows when shot and fight on oblivious to the flesh wounds.
The source of these armors was unclear; although it was most likely Japan: (1) there had been active trading between the Cheng Clan and Japan since the days of Koxinga's father, 鄭芝龍Cheng Zhi-long (1604-1661), who controlled the eastern seas of China; (2) Koxinga himself had grown up in Nakasaki, Japan, who might have seen the armored samurai in action; and (3) the face masks were known to be worn only by the Japanese (not Chinese) warriors. The picture on the above left, i.e., a 16th Century armor-suit worn by a high-ranking samurai, might have been just that used to outfit the Iron-man soldiers [without the arm and leg guards].
The selection of these men was quite rigorous. Each recruit must be able to carry a certain weight and with it ran a certain distance to qualify. Power and endurance were both prerequisites for wearing the heavy armors (weighing about 33 lbs) and fighting at the same time. About 5,000 were chosen during the first screening. Some reports mentioned Japanese and Caucasian participants. That would not be so surprising as the Cheng army did invite other people than the Hokkienese to join up.
This special force, numbering about 3,000 (up to 10,000), was part of the 左 and 右虎衛營 [Left and Right Tiger Guard Battalions] under the direct command of Koxinga. Its basic unit was a 6-man squad equipped with the heavy sword 雲南斬馬刀 (2), shields (2), bow and arrow sets (6). Also, for each 10 squads, 4 specialized in attacking with bow and arrow and the other 6, sword and shield. They were trained to fight as one, any disruption to the formation, by either advancing or retreating, especially the latter, was severely punished. On the other hand, they were handsomely rewarded after each victory and were paid 3 silver taels each month [double the regular army pay].
The unique weapon here was the razor-sharp 雲南斬馬刀 or Yun-nan horse-slaying saber-sword. Yun-nan was just its name, had nothing to do with the Yun-nan province. Legend has it that each blade was made by passing serially through 100 iron-smiths who hammered it into shape. This may have been a process similar to the samurai-sword-making in Japan, a long piece of soft iron core folded onto itself thousands of times (to give it flexibility) which was then encased in a hard steel shell (for sharpness and strength). And this is done by only one master plus 1-2 assistants. With 100 masters working at the same time, mass-production of the horse-sabers was therefore possible.
The Dutch defenders of Zeelandia had calculated that one Dutch soldier could fend off 25 of Koxinga's iron-men. They were fatally mistaken.