The ring mount was designed by both Elco and Bell, and designated Mark 17 Twin 50 caliber aircraft mount. Part of the Mark 17 Mod 1 and Mod 2 ring mount consisted of the Bell Mark 9 twin cradle
.50 cal Machine
Gun Turrets
Common to all U.S. PT boats were dual Browning M2 .50 cal machine guns mounted in two open ring, rotating turrets. These were used for anti-aircraft defense and general fire support.