Nakajima KI-27 "Nate" used by the Royal Thai Air Force. 

The RTAF

Japanese Type 89 grenade launcher - also known as the "knee mortar" in (correct) use by Japanese soldiers in China, 1942.  The name "knee mortar" apparently came from an initial US misunderstanding of the Japanese protocol for carrying the weapon, from the belt, down against the thigh.  This misunderstanding, and the fact that the base plate of the weapon apparently facilitated its use balanced on the knee, led a number of US Marines to experiment with captured Type 89s elevated over the top of the knee - experiments which resulted in a number of broken thighs, separated knees, and other serious leg injuries.  The misunderstanding was quickly cleared up, and the use of captured Type 89s from the knee was, thereafter, firmly discouraged.  Best regards, JR.

Type 89 grenade launcher.

The Chinese Vickers Mk.E Type B destroyed in Shanghai and captured by the Japanese.