Bang for the Buck origin

Thanks in advance for your help determining the origin for the phrase, 'Bang for the Buck'. One explanation is that it developed from the military as a phrase for exlaining relative value i.e. The missile carrier has more BFTB an a tank. However, to me this explains the usage of the phrase, not it's actual origin.

Another source suggested the phrase relates to the slave trade in referring to the reproductive value of a male slave, otherwise known as a buck. This possible explanation could be considered offensive. For that reason, I've asked colleagues to refrain from using it. Hopefully someone can offer some substantive evidence about its derivation. Many thanks,

Dina