The Gatling Spear Gun is a weapon found only in Ninja Gaiden II. Unlike the Spear Gun from the previous game, this type is only usable underwater. The spear gun is found in Chapter 5: The Aqua Capital in a chest next to the underwater tunnel. It is ideal for taking out Gaja or sea serpents. The Gatling Spear Gun was removed from Ninja Gaiden Sigma 2 and the slot for it is just left empty.
Because the spear gun fires rapidly, firing at the sea serpents close to the edge of water with Ryu's head sticking out is a great way for a 100 hit-combo.
Ryu wields this weapon as if he was holding a Gatling machine gun, except he cranks it up to fire.
Quoted from Ninja Gaiden II:
"A Gatling-type Spear Gun designed for underwater combat. It is practically useless on dry land. A prime example of an OOPArt (out of place artifact), the Gatling Spear Gun was made in 10th-century Europe. It is fired by turning the handle, which engages a high-pressure water pump to force projectile spears out of its barrel. At first glance, one would expect the spears to be subject to extreme amounts of drag, but in fact they are able to ”fly” through the water due to the phenomenon of supercavitation. The spears are loaded with explosive material and burst after hitting their target, shredding it from the inside out."
- It is the only weapon removed from Sigma 2 that has no data left in-game, unlike the Windmill Shuriken and Incendiary Shuriken, that can still be used by modifying savedata.