Iowa State Register reports that Martin Harris said that Joseph was given the Urim and Thummim to translate the BOM.
“A Witness to the Book of Mormon,” Iowa State Register (Des Moines), August 28, 1870, in Dan Vogel, ed., Early Mormon Documents, 5 vols. (Salt Lake City: Signature Books, 1998), 2:330
There was also found in the chest, the urim and thummim, by means of which the writing upon the plates was translated, but not until after the most learned men had exhausted their knowledge of letters in the vain effort to decipher the characters. It had been revealed to Joseph Smith that the writing upon the tablets contained a history of the aborigines of this country down to the time of Columbus’ discovery, and after, all human means had failed to secure a translation, Smith was commissioned to undertake the task. By means of the urim and thummim “a pair of large spectacles,” as Mr. Harris termed them, the translation was made, and Mr. Harris claims to have written, of the translations as they were given by Smith, “116 solid pages of cap [foolscap].” The remainder was written by others.