> A gun's "singular purpose" is not to sling lead. It's to sling lead at an enemy, which means slinging lead on a battlefield, and those are far more complex and multifarious tasks than you're making them out to be. The navy ditched it because it turned out to be useless against WWII-tech aircraft. The army was about to ditch it because the water-cooling setup was too finicky and vulnerable and it couldn't be mounted on anything useful.
But I think the point the above poster was making is, those deficiencies you listed was due to the obsolescence of continuing to use a .50 caliber round in that role. The M2 fulfilled its role as a .50 caliber machine gun continuously. Sure, it may have originally been designed as an anti-tank gun and by the time it saw major service using .50 caliber rounds for anti-armor was totally deficient. But the guns found other niches like vehicle mounts and aircraft mounts in its lightened version. I think you're indexing a bit too heavily on the fact that water cooling was ditched. Air vs. water cooled isn't an especially large design change - just rip out the water jacket and replace the jacket with a barrel shroud if needed. It's more a trade-off between mobility and ability to sustain fire, and as the battlefield changed an air cooled variant became better suited. The fact that an M2 mounted on a Stryker is nearly the same overall design as the one originally developed for WW1 is still impressive. The only substantive change to how it operates that I know of is the addition of a bi-directional feeding mechanism.
> It's more a trade-off between mobility and ability to sustain fire,
If the design were really the ideal of the perfect tool that only cares about exactly one simple task, these trade-offs wouldn't exist. These items haven't been in service for so long because they sprang fully-formed from the designer's mind with perfect purity of purpose. They've been in service for so long because they were flexible enough to support a literal century of refinement, adaptation, and evolution. The M2 was originally water-cooled because it was meant to be a fixed weapon in emplacements or on ships. They rebuilt it with air-cooling because they needed a gun to put on a tank and it turned out that it was useless on ships. Then they made it fire faster because they needed guns to put on airplanes. Then they added a quick-change barrel system because they needed extended courses of fire. Then they completely redesigned the bolt and chamber because modern machine tools allowed them to use a cheaper, more reliable, and more maintainable design. Then they changed some of the ergonomics to improve mobility and barrel-changing even further. You don't actually want an "original M2". Those were junk, everyone knew they were junk, and it twenty years for them to stop being junk. What the parent is thinking of as the "original, basic M2" is the one with twenty years of adaptations and refinements, and that puts a very neat hole in the entire idea that the pattern was somehow endowed with some kind of lost simplicity. The original M2, compared to the version the OP is thinking of, is just as obsolete and dated as the original iphone is now.
The quick change barrel was introduced in 2010. We're still talking close to a century before substantive changes were made to the design. The "Original M2" as most people know it was air cooled, had bi-directional feed, and is very much the same as the ones in service today aside from the shift away from adjustable head-spacing in 2010. The designation "M2" does not refer to the water cooled M1921, but the air cooled version produced after Browning's death [1]. I guess if you want to stretch back the age of the M2 an extra decade you can highlight the ancestry of the design back to 1921 (usually people do this to give credit of the gun to John Browning, similar to how people say the Hi-Power was designed by browning) but bear in mind that the M1921 is not what most people think of as the original M2. They're thinking of the 1933 gun.
I'm not sure where you got the idea that "those were junk, everyone knew they were junk, and it [took] twenty years for them to stop being junk". Strange for a gun that was "junk" to be adapted for use by foreign companies only 6 years after release[2], and imitated by other foreign powers[3] less than 10 years after release. For a gun that was such junk, other countries were eager to imitate it. The M2 was a particularly effective and long-lived design, and one that went largely without adaptation since its initial release in 1933. What other piece of equipment is so similar to its original design from over 80 years ago?
Hmm, you're right, I think that I lost my train of thought here. Let me start over.
I understand that the M2 that we all think about is an excellent design, but claiming that it was an ideal pattern from first conception is incorrect, and comparing it to the iphone of all things is asinine. I wouldn't have complained as much if it'd been compared to, say, a Pixel 1 or iPhone 6, since it is annoying that those stopped getting software updates after only 2 or 3 years when smartphones as a concept are only 12 or 13 years old. But comparing the M2 to a first-of-its-kind transformative revolution, then complaining that the revolutionary front-runner was obsoleted in a hurry? Duh. That's what happens when you find a new region of configuration space. The M2 was not in any way something you could hold up as an "original". It was not the first gun to use its action, it was not the first in its role, it was not the first in its class or type, it wasn't even the first to use its cartridge. It was the very end of a long process of refinement.
If you want to compare cell phones to firearms, you shouldn't be using guns from the 1930s as examples. You might as well compare it to the early telegraphs, which had one wire per letter, signaled by electrolyzing bubbles of hydrogen out of a vial of acid, and could barely go from one room to the next because they didn't have high-voltage sources or relays. You should be looking at firearms from the 1890s.
The Maxim gun came out in 1884 and revolutionized the concept of the firearm. It blew up. Everyone started trying to improve on it and refine it. And they did, in all sorts of crazy ways that were obsolete almost before they'd left the factory. We didn't start seeing solid designs until things like the luger in 1989 and the springfield in 1903. By the outbreak of WWI the Maxim gun was thoroughly obsolete, though it did have descendants. Not only are modern electronics more complex, with vast design spaces to explore and multiple orders of magnitude more room to improve into, we're barely 12 years past our Maxim gun equivalent. We'll remember the iphone forever, but it was no more timeless than the Maxim gun was, and I doubt we'll see a "timeless" cell phone for at least another decade. Maybe two. Or maybe the entire idea of the cell phone will turn out to be a an inefficient, clunky in-between that'll go the way of water-cooling.
> "those were junk, everyone knew they were junk, and it
> [took] twenty years for them to stop being junk".
Turns out I did misread something, sorry; I'd lost a comma on the wiki page and thought the air-cooled version hadn't been introduced until the start of WWII. Even using the 1933 version, though, it's still more than a decade from the first labeled pattern of the gun in 1921, which was... not great.
I don't think anyone is citing the M2 as some sort of transformation or as a novel design - just as an especially long lived one. There's not much novel about it. It's essentially just a scaled up M1919 (which is itself essentially an air cooled version of the M1917) machine gun.
But I think the point the above poster was making is, those deficiencies you listed was due to the obsolescence of continuing to use a .50 caliber round in that role. The M2 fulfilled its role as a .50 caliber machine gun continuously. Sure, it may have originally been designed as an anti-tank gun and by the time it saw major service using .50 caliber rounds for anti-armor was totally deficient. But the guns found other niches like vehicle mounts and aircraft mounts in its lightened version. I think you're indexing a bit too heavily on the fact that water cooling was ditched. Air vs. water cooled isn't an especially large design change - just rip out the water jacket and replace the jacket with a barrel shroud if needed. It's more a trade-off between mobility and ability to sustain fire, and as the battlefield changed an air cooled variant became better suited. The fact that an M2 mounted on a Stryker is nearly the same overall design as the one originally developed for WW1 is still impressive. The only substantive change to how it operates that I know of is the addition of a bi-directional feeding mechanism.