An apparatus for releasably mounting an auxiliary compressed air tank to a breathing apparatus of the type having a main compressed air tank is provided. The apparatus includes a bracket having a pair of mounting legs connected in relatively closely spaced facing relation to one another defining a strap receiving area and means for clamping one of the mounting legs rigidly with the other mounting leg spaced outwardly therefrom. One of the mounting legs is selectively insertable and removable from a disposition between the main compressed air tank and a securing strap of a harness which supports the main compressed air tank on a user. The harness strap is received in the strap receiving area and the strap is tightened to hold the auxiliary tank relative to the main tank. To release the auxiliary tank, the strap is loosened and the mounting leg is moved to clear the strap.