The P-38 is known as a "John Wayne" by the U.S. 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, 38mm, in length) and consists of a short metal blade that serves as a handle (which doubles as a flat-blade screwdriver), 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.

Official military designations for the P-38 include 'US ARMY POCKET CAN OPENER' and 'OPENER, CAN, HAND, FOLDING, TYPE I'. As with some other military terms (e.g. jeep), the origin of the term is not known with certainty; the P-38 opener coincidentally shares a designation with the P-38 'Lightning' fighter plane, which could allude to its fast performance. However, the P-51 can opener, while larger and easier to use than the P-38 can opener, also has a fighter plane namesake in the P-51, which is faster and smaller than the P-38 fighter. One rumored explanation for the origin of the name is that the P-38 is approximately 38 mm (1.5 in) long. This explanation also holds for the P-51, which measures approximately 51 mm (2.0 in) in length. U.S. Army sources, however, indicate that the origin of the name is rooted in the 38 punctures around the circumference of a C-ration can required for opening.

P-38s are no longer used for individual rations by the United States Armed Forces, as canned C-rations were replaced by uncanned MREs in the 1980s. The larger P-51s are, however, included with US military "Tray Rations" (canned bulk meals). They are also still seen in disaster recovery efforts and have been handed out alongside canned food by rescue organisations, both in America and abroad in Afghanistan. The original US-contract P-38 can openers were manufactured by J.W. Speaker Corp. (stamped "US Speaker") and by Washburn Corp. (marked "US Androck"), they were later made by Mallin Hardware (now defunct) of Shelby, Ohio and were variously stamped "US Mallin Shelby O." or "U.S. Shelby Co.".