Marathon General Purpose Mechanical Review: Built for Battle, Worn for Fun

For way too long, I’ve had a deep curiosity with testing out the 34mm Marathon General Purpose Mechanical. From afar, you can tell that it isn’t trying to do anything clever. No frills, no confusion, no need to justify its presence with some contrived design story or lifestyle fantasy. Getting this one in for review only reinforced some of my assumptions of the watch while bringing some surprises with it. The thing wears its purpose on its sleeve (and on its caseback, dial, and strap, for that matter). It’s not trying to be a daily diver, a weekender, or a dress watch in disguise. But it does its job and that’s what people are typically looking for in a watch like this.

The Marathon GPM is one of those watches that still gets made to military spec, not just made to look the part. Marathon is one of the few brands that still delivers timepieces to actual government agencies, and that real-world credibility adds a layer of appeal that goes way beyond looks. We’ve reviewed some great models before. The one I had on wrist was a review unit straight from the brand, and while I’ll eventually have to send it back, I enjoyed my time with it way more than I thought I would.

On paper, a 34mm case diameter might seem like a dealbreaker for a lot of modern collectors. But honestly, that number barely registers once it’s strapped on. The 12.5mm thickness, combined with the 41mm lug-to-lug and a beefy NATO strap, gives the watch a surprising amount of wrist presence. It wears compact, yes, but not dainty. The sage green case lands right where it needs to—a foresty greenish-grey tone that leans utilitarian without being boring. The resin material keeps things lightweight, and if you’re used to big steel cases, this one might make you rethink how you define “tough.”

There’s a blunt honesty to the caseback that I really appreciate. Instead of marketing fluff or decorative flourishes, you get the straight-up military spec text and NSN (NATO Stock Number) info. It’s functional documentation. I wish more brands would take that approach. Same goes for the bezel, which isn’t there to rotate or dazzle—just to frame the crystal and keep everything locked in place. Even the crown feels like it’s been dialed in specifically for function: all steel now (a welcome upgrade over Marathon’s older plastic ones), it winds easily and feels right-sized for the case. Oh, it doesn’t screw down and water resistance is only 30m. Not bad for a field watch but I’d like to see this increased to 50m in the future. The crown is also quite grippy and even though it may look small, it was super effective any time I had to interact with the watch.

Of course, the star of the show here—as with many Marathons—is the dial visibility. It’s built around a classic field layout with a 24-hour inner ring and just enough branding to let you know what you’re looking at without turning it into a billboard. The tritium tubes are a big part of that legibility. Set into the hour markers and both syringe-style hands, they glow with that bright, perpetual radioactivity that doesn’t need charging. Even indoors during the day, you catch glimpses of the lume doing its job. There’s real depth to the dial because of that, which adds a lot more character than you’d expect from something this utilitarian. If you’re ever curious about what it takes to manufacture these tritium gas tubes before integrating them into a watch, check out our interview with Barry Cohen, who is currently running the ProTek watch brand.

Now, about that strap. The supplied ballistic nylon one from Marathon looks great, no question. The brown tone pairs nicely with the case and gives the whole thing a sort of field gear vibe. But functionally, I found it a bit stiff out of the box. The clearance between the spring bars and case is tight, and getting everything situated took more effort than I’d like. Threading through the keeper was a bit of a chore, too. That said, I did try the GPM on a single-pass olive drab strap, and that was the sweet spot. It let the case sit lower and just felt a touch more wearable. Do realize that the 16mm lug width may make things tough, since it isn’t really a common width for straps these days. Thankfully, I had something a little more comfortable in the strap drawer.

Inside, you’re getting the ever-reliable Seiko NH35A. It’s not exotic or high-end, but it’s one of those movements you can trust to just work. With 41 hours of power reserve, the one in this GPM ran great day-to-day. I didn’t hook it up to a timegrapher, but nothing jumped out as off. It’s also the kind of movement that, if it ever craps out, you could just swap with a fresh one without thinking twice. That’s the beauty of something this accessible.

Living with the GPM over the course of the review left me with one thought: I get it. I get why this watch exists, why Marathon still makes it, and why it’s held in such high regard by folks who actually rely on their watches to do more than just tell time stylishly. It’s the real thing, still doing the thing. And while this unit is headed back to Marathon soon, I wouldn’t be surprised if another one makes its way into my collection. It’s just too simple and too satisfying not to own at some point.

Marathon