Hamilton Revives a Rare Vietnam-Era Grail Watch to Celebrate America’s 250th Birthday

Hamilton’s Khaki Field Watch is no slouch. If you’ve spent any time on our site, you’ll know how much we love and respect the American-turned-Swiss watchmaker’s flagship field watch. From the First World War through the conflict in Vietnam, Hamilton equipped U.S. troops with rugged, highly-legible timepieces that weren’t too big in size. Offered to civilians in the ’80s as the Khaki Field Watch, these wristwatches have only increased in popularity over the decades, with a full reissue in 2018 pushing the model even further into icon status.

For its latest iteration, Hamilton is going back to its period-correct dimensions. This is one of the few times a Khaki Field Mechanical has gone down to its proper 36mm sizing (rather than the typical 38mm), and it’s here to celebrate America’s 250th birthday this year.

Holy Grail Material

To understand what Hamilton pulled off here, you have to know the backstory. In 1970, with the Vietnam War still raging and the U.S. Air Force requiring more precise, legible timekeeping for its navigators, Hamilton developed the FAPD-5101. This was not just your ordinary field watch but was purpose-built for aerial navigation duties, where timing was critical for fuel calculations, rendezvous, and bomb runs. The watch featured a 36mm parkerized steel case, slightly larger than most MIL-spec watches of the era, and was powered by the Caliber 684, a 17-jewel hand-wound movement developed exclusively for this reference. It never appeared in another Hamilton watch, before or since. Production was limited, the window of issuance was narrow, and surviving examples are rare enough that the FAPD-5101 has achieved grail status. That’s the watch Hamilton is pulling from the archives for America’s 250th.

Back to 36

The new Khaki Field Mechanical 250 checks a lot of the same boxes as its source material. The 36mm stainless steel case wears a matte bead-blasted finish, measuring 10.2mm thick with an 18mm lug width. The case is fitted with fixed spring bars, which is both a period-correct detail and a practical one: it eliminates the vulnerability of standard spring bars entirely. The trade-off is you’re limited to NATO and pass-through straps, though Hamilton thoughtfully includes two of them, an olive-green nylon and a brown calf leather, alongside a green rip-stop nylon watch roll.

The crystal is acrylic, not sapphire, and it’s the box-shaped variety to match the original. Hamilton applies a hard coating and anti-fingerprint treatment. Inside there’s also a dust cover, a direct nod to the anti-magnetic, dust-resistant construction of the original FAPD-5101 that was built to survive cockpit conditions. The crown is notably shorter in profile than what you’ll find on the standard Khaki Field Mechanical, but wider with a more pronounced fluted grip, designed for operation with gloves on.

Same Spirit, Different Engine

Where the modern version departs from the original is under the caseback. The FAPD-5101’s Caliber 684 was a singular movement, developed just for that watch. However, the Khaki Field Mechanical 250 runs Hamilton’s H-50, a manual-wind caliber based on the ETA C07.701 platform, with 21,600 vph frequence and an 80-hour power reserve. It’s fitted with a Nivachron balance spring for magnetic resistance, which the original dust cover was also designed to address.

The dial stays faithful to the original in matte black paired with white numerals, a 24-hour inner track, and triangular hour markers filled with Super-LumiNova Grade X2 in that characteristic warm pumpkin-yellow tone that recalls vintage tritium capsules. Hamilton adds its retro wordmark to the dial, which the original never had, and engraves the caseback with commemorative text detailing the watch’s American homage and limited status.

Spec Sheet

Pricing & Availability

The Khaki Field Mechanical America 250 Anniversary Edition is priced at $725 and is limited to 1,776 pieces, a nod to the year the Declaration of Independence was signed. It’s available exclusively in the United States through Hamilton. A non-limited 36mm version is available to global markets, and Hamilton is producing a version with a generic caseback engraving for international customers, without the leather strap or commemorative packaging.

Recap

Hamilton Khaki Field Mechanical America 250 Anniversary Edition

In time to celebrate America’s birthday, Hamilton’s Khaki Field Mechanical 250 is a limited-edition field watch built around the rare FAPD-5101 navigator’s watch from 1970, scaled down to a period-correct 36mm.

Learn More: Hamilton