- Admiral Kirk and his command crew travel back to this year to retrieve a pair of humpback whales in order to answer the call of a mysterious probe assaulting Earth in 2286. They take George and Gracie, along with a cetacean biologist, Dr. Gillian Taylor, back with them. During the acquisition of the whales, Montgomery Scott and Leonard McCoy provide Dr. Nichols with the formula for transparent aluminum on his Macintosh computer. (Star Trek IV: The Voyage Home)
Background information Edit
Note the possibility of a time paradox, if Nichols' acquisition of the formula from Scotty resulted in his original invention of the material.
The date on the San Francisco Register was Thursday, December 18, 1986. This date is correct for that year. . However, a prop for the pawn shop ticket for Kirk's glasses was on display at Star Trek: The Experience (but not seen on screen) was dated 19 August 1986, suggesting that the two days over which these events took place were August 19 and 20. 
- Star Trek IV: The Voyage Home (in part)