10th Mountain Div. jeep in Italy, 1945.
The bracket will hold the jerry can facing in either direction. Drivers were instructed to mount the can with the opening away from the exhaust pipe to reduce the risk of gas touching the hot pipe. This correct procedure was far from universally followed so you may see photos of jeeps or trucks with the can mounted either way.
This bracket is commonly associated with the back panel of WW II Army jeeps. However, the gas can was not developed until after the jeep went into production early in World War II. Therefore, early jeeps did not have a gas can bracket unless one was added later. According to the g503.com web site, Willys started installing the bracket in June 1943 with MB serial number 165582.
As seen in the top photo on this page, the M-151 series of 1/4 ton 4x4 trucks (jeeps) did not use a bracket shell to hold the gas can. Instead, the can sat on top of the left rear bumperette and was secured to the vehicle with a specially designed strap, as illustrated in the diagram to the left. Two straps attached to the jeep body with footman loops (4) near the bumperettes. Those two straps joined at a center ring with another vertical strap ending in a buckle (2). A separate strap (1) crossed over the top of the gas can to the buckle to complete the tie down.
This method was only used on the M-151, M-151A1 and M-151A2 models. Other models of the series -- such as the M718 ambulance -- used the traditional "Bracket, Drum, Fuel Can Mounting" with NSN 2590-00-473-6331.
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