The Flat-Pack, Can-Do Opener: 38+ Uses for the “Best Army Invention Ever”

The P-38‘s creator probably never imagined that the little can opener he devised during World War II would go on to become one of the 20th century’s most useful and portable multi-tools.

Inventor Major Thomas Dennehy alongside instructions and packaging for the P-38 can opener

In the days before MREs, the P-38 was designed to open K-ration cans. Major Thomas Dennehy of the Subsistence Research Laboratory in Chicago invented it in just 30 days during the summer of 1942. The bladed part flips out for use, then packs flat for travel. It is also engineered not to break, rust, require sharpening or need polishing.

“The P-38 is one of those tools you keep and never want to get rid of,” reports United States military policeman Sargent Scott Kiraly. And thanks to a punched hole that lets it hang alongside dog tags or attach to a key ring, it’s easy to keep one of these handy at all times.

Though accessing food was its main design purpose, the device is much more than just a can opener — by one man’s count, it actually has more than 38 uses (though to be fair, a few of them are pretty specific). Per Steven Wilson of the Department of the Army Office of the Chief of Chaplains at the Pentagon, these include:

1. Can Opener
2. Seam Ripper
3. Screwdriver
4. Clean Fingernails
5. Cut Fishing Line
6. Open Paint Cans
7. Window Scraper
8. Scrape Around Floor Corners
9. Digging
10. Clean Out Groove on Tupperware lids
11. Reach in and Clean Out Small Cracks
12. Scrape Around Edge of Boots
13. Bottle Opener
14. Gut Fish (in the field)
15. Scale Fish (in the field)
16. Test for ‘Doneness’ When Baking on a Camp Fire
17. Prying Items
18. Strip Wire
19. Scrape Pans in the Field
20. Lift Key on Flip Top Cans
21. Chisel
22. Barter
23. Marking Tool
24. Deflating Tires
25. Clean Sole of Boot/Shoe
26. Pick Teeth
27. Measurement
28. Striking Flint
29. Stirring Coffee
30. Puncturing Plastic Coating
31. Knocking on Doors
32. Morse Code
33. Box Cutter
34. Opening Letters
35. Write Emergency Messages
36. Scratch an Itch
37. Save as a Souvenir
38. Rip Off Rank for On-the-Spot Promotions
39. Bee sting removal tool (scrape off w/ blade)

The little gadget’s name has a contested origin story. Some say it derives from the roughly 38 punctures needed to open a can. Others claim that P-38 is a reference to an ultra-fast fighter plane of the same designation. The device is also around 38 millimeters long. It has been dubbed the “John Wayne,” too, for its toughness and dependability.

“There have been other inventions that Soldiers came to cherish,” Renita Foster of Fort Monmouth Public Affairs wrote in an article titled The Best Army Invention Ever. These include the “steel helmet that proved ideal for washing, shaving, and cooking; the faithful, trustworthy jeep, guaranteed to go anywhere in any kind of weather; and the TA-50 ammunition pouch for storing those personal items soldiers just couldn’t leave behind.” But for many soldiers, the P-38 is a particular favorite, in part because of its many everyday uses.

The U.S. Army continued to use P-38s up through the 1980s for C-ration cans, and still distributes a larger version (the P-51) in some cases along with meals and as part of disaster relief efforts. A number of companies sell both the P-38 and P-51 online, too.

Special thanks to Sam del Rosario for sending in this story idea!

  1. Grant Shipley

    The TSA won’t allow you to take a P-38 on a plane. I know, I tried to take my faithful P–38 with me, but: No.

  2. Christian

    In the Australian Army it was known as the FRED – F*&king Ridiculous Eating Device – I still have a couple, they are the best tool

  3. Lester Rhetoric

    I still regularly use the one I got in the service back in the 1970’s. It works great, never rusted, and never needed to be sharpened.

  4. Darryl

    One thing a previous commenter didn’t mention about the Australian version of this device is that they built another function in to it. On one end you have the cutting device, and the other has been formed in to a shallow spoon so you can also eat with it.

  5. Peter

    “38+ uses!” (Why not just say “39!”?) Well over half of which could be done with a bare hand. This is far from number one. #woobie

  6. Kenneth Howard Whitman

    Sat. 3/6/2021, I still have mine issued to me at Ft. Jackson, SC in Sept.1962. It has 1961 mfg. date, also
    US. G.G. Greene on it. It’s irreplaceable, it’s a sentimental thing.

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