Ninja Gaiden III: The Ancient Ship of Doom

Ninja Gaiden III: The Ancient Ship of Doom is the final game in the original Ninja Gaiden trilogy for NES. The game takes place between the first two titles in the series and focuses on Ryu trying to clear his name after being accused of murdering his CIA partner, Irene Lew. 

The game updated the series by adding a sword power-up mechanic, and allowing Ryu to cling to and move along horizontal ceilings. The clone mechanic from Ninja Gaiden 2 is no longer present.

A big change to this game is the differences between the Japanese and American versions. The original Japanese release was made to be easier than the original two games which were considered to be too difficult for Japanese gamers. While Taito America made the game much more difficult than it's predecessors because they assumed that's what players wanted. Because of this, the damage Ryu takes from enemies is doubled, the password continue feature is removed, and the player is only allowed 5 continues instead of the infinite allowed in the Japanese version.

Though this ends a trilogy the series is continued with Ninja Gaiden on the Xbox. 

An update of the game was release as part of the SNES title Ninja Gaiden Trilogy. Ninja Gaiden 3 is available on the Wii Virtual Console.