ABC had trouble filling the 8:30 (ET) slot on Fridays in the late 60's until The Brady Bunch came along at the end of the decade. The 1967-8 season started with Hondo, which lasted half a season, in the slot.
In January 1968, Hondo was booted, and the replacement came from a more reliable supplier, that being game show mogul Chuck Barris.
Barris saw how Bob Hope was having success with his USO tours of Vietnam, so he and Bill Carruthers pitched the idea to ABC of a weekly variety show that visited various military bases around the country.
Unfortunately, Operation Entertainment, while it ran for parts of two seasons, isn't as well remembered as Barris' greater successes, including The Dating Game, The Newlywed Game, and, of course, the iconic 70's classic, The Gong Show, which has found new life as a summer series on ABC, now in its 2nd season.
While there was a guest host every week, Barris had his favorites, including Dating Game host Jim Lange and actor-comedian Tim Conway, who each had multiple appearances.
I don't remember seeing the show, so there's no rating. We'll leave you with this clip with host du jour Dick Cavett introducing Louis Armstrong at Fort Hood in Texas.