The IKS Klothos was a Klingon battle cruiser that was in service with the Klingon Imperial Fleet in the late 23rd century. Klothos was commanded by Kor when he was in charge of the first of two Klingon divisions (the second being commanded by Kang) to participate in an attack against the Federation outpost at Caleb IV, successfully implementing the military stylings of an ancient Earth cavalry attack. The cloaking device was a new piece of technology to the Klingons at the time, and Kor was said to have spent three days in the engine room studying the device aboard the Klothos before the mission. (DS9: "Once More Unto the Breach")
Serving under Kor aboard the Klothos in 2269 were his first officer Kaz, and crewwoman Kali. The Klothos engaged the USS Enterprise in the Delta Triangle region, and both ships were pulled into the "triangle" during the battle. The crews of the Enterprise and Klothos were able to make a successful escape once they were able to set aside their differences and work together. (TAS: "The Time Trap")
Template:D7ClassStarships
Appendix
Background information
In the 1998 episode "Once More Unto the Breach," an aged Kor said that the Klothos was a D5 class vessel. When the ship was seen in the 1973 episode "The Time Trap", she appeared to be a slight variant of the D7 class. It should be noted that the actual design of the D5 class was not introduced on-screen until the 2002 episode ENT: "Marauders".
A number of explanations are possible for this retcon. There could have been two different vessels with the same name commanded by Kor (just as James Kirk commanded two ships named Enterprise) or D5 might also be a 23rd century designation for a variant of the D7 class. Or, as the senility of Kor was the key focus of the DS9 episode's plot, he might have simply been confused with the class name of his old ship.
The incident at Caleb IV was not given a date in "Once More Unto the Breach," though it must have occurred at some point before peace was made between the Klingon Empire and United Federation of Planets in 2293. Kor however attributed the swift victory to the fact that Federation did not yet know Klingon ships to possess cloaking technology. It therefore propably occurred prior to "The Time Trap" as the Klingon ships were at the time already assumed to have a cloaking device.