COOL MUSIC VARIETY: Dick Haymes performing You'll Never Know was made during the...

FYI: Dick Haymes, The Song Spinners performing You'll Never Know was made during the 1942–1944 musicians' strike, an American Federation of Musicians strike against the recording companies. As a result, the recordings were made without musicians, with vocal groups replacing the usual instrumental backup. 

The group backing Haymes, The Song Spinners, was actually given credit on the Haymes record. (The Song Spinners #1 hit, "Comin' In on a Wing and a Prayer" held the #1 spot on the charts for three weeks preceding Haymes' "You'll Never Know." Vocalist Margaret Johnson of The Song Spinners did the vocal arrangements for both songs.)

https://en.wikipedia.org/wiki/You%27ll_Never_Know