Both responses sound weird to me. I think it should be "It was not mentionED how long the rescue operation was"

Thanks a lot Phil, Adrian, Ian Noel Morrison If you let me , I conclude correct reply is: How long did it take the rescue operation team ( mission) to save Tong Tong? It wasn't mentioned how long the rescue mission( operation) took Is it correct?!

It is not mentioned how long the rescue mission was. You can search on-line for "embedded questions." It's actually a type of subordinate clause that functions as a noun.

How long did it take the rescue operation team to save Tong Tong ? It is a question , asking how long it took .