P-38 C-Ration Can Opener
 
The P-38 is known as a "John Wayne" by the United States Marine Corps, either because of its toughness and dependability, or because of an unsubstantiated story that the actor had been shown in an as-yet-unidentified training film opening a can of K-Rations. The can opener is pocket-sized, approximately 1.5 inches (38 mm) long, and consists of a short metal blade that serves as a handle, with a small, hinged metal tooth that folds out to pierce the can lid.
A notch just under the hinge point keeps the opener hooked around the rim of the can as the device is "walked" around to cut the lid out. The handle portion can also double as a makeshift flat-blade screwdriver, with limited ability because of the rather soft sheet metal used. 
One technical explanation for the origin of the name is that the P-38 is approximately 38 millimetres long. However, use of the metric system in the US was not widespread at this point, and United States Army sources indicate that the origin of the name is rooted in the 38 punctures around the circumference of a C-ration can required for opening.[1]
 They are also still seen in disaster recovery efforts and have been handed out alongside canned food by rescue organizations, both in America and abroad in Afghanistan.
The original U.S.-contract P-38 can openers were manufactured by J.W. Speaker Corporation of Germantown, Wisconsin (stamped "US Speaker") and by Washburn Corporation (marked "US Androck"); they were later made by Mallin Shelby Hardware inc (defunct 1973) of Shelby, Ohio and were variously stamped "US Mallin Shelby O." or "U.S. Shelby Co."