Casio G-Shock GA-B2100 CasiOak vs Hamilton Khaki Field Automatic
Casio's diver meets Hamilton's field watch
Quick Verdict
The Casio G-Shock GA-B2100 CasiOak ($100–$150) offers Casio Quartz (Solar-Powered) precision in the tier below the Hamilton Khaki Field Automatic ($500–$1,000). The G-Shock GA-B2100 CasiOak measures 45.4mm (48.5mm lug-to-lug, 11.9mm thick) and is rated 200m (20 ATM). The Khaki Field Automatic counters with Swiss Made craftsmanship and 100m (10 ATM) water resistance. Both are exceptional watches for their respective tiers.
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Specifications Compared
| Feature | Casio G-Shock GA-B2100 CasiOak | Hamilton Khaki Field Automatic |
|---|---|---|
| Price | $100–$150 | $500–$1,000 |
| Case Size | 45.4mm (48.5mm lug-to-lug, 11.9mm thick) | 38mm |
| Movement | Quartz Module 5689 (Tough Solar + Bluetooth) | Automatic H-10 |
| Caliber Type | Casio Quartz (Solar-Powered) | Automatic (ETA C07.611 base) |
| Power Reserve | About 7 months on a full charge without light; about 18 months in power-saving (Casio) | 80 Hours |
| Water Resistance | 200m (20 ATM) | 100m (10 ATM) |
| Crystal | Mineral Glass | Sapphire Crystal |
| Case Material | Carbon Core Guard Resin | Stainless Steel |
| Origin | Made in Japan | Swiss Made |
Category-by-Category Analysis
Design & Aesthetics
Casio's design language vs Hamilton's approach
The Casio G-Shock GA-B2100 CasiOak features a Carbon Core Guard Resin case at 45.4mm (48.5mm lug-to-lug, 11.9mm thick) with Mineral Glass protection. The Hamilton Khaki Field Automatic offers Stainless Steel construction at 38mm with Sapphire Crystal. Both represent their brand's distinct design philosophy and heritage.
Movement & Performance
Quartz Module 5689 (Tough Solar + Bluetooth) vs Automatic H-10
The G-Shock GA-B2100 CasiOak runs the Quartz Module 5689 (Tough Solar + Bluetooth) (Casio Quartz (Solar-Powered), About 7 months on a full charge without light; about 18 months in power-saving (Casio) power reserve) at standard frequency. The Khaki Field Automatic uses the Automatic H-10 (Automatic (ETA C07.611 base), 80 Hours reserve) at 21,600 vph (3 Hz). The Khaki Field Automatic offers a longer power reserve.
Wearability & Fit
45.4mm (48.5mm lug-to-lug, 11.9mm thick) vs 38mm — different wrist presence
At 45.4mm (48.5mm lug-to-lug, 11.9mm thick), the G-Shock GA-B2100 CasiOak has a bolder wrist presence compared to the Khaki Field Automatic at 38mm. Water resistance differs: 200m (20 ATM) vs 100m (10 ATM).
Value & Cost of Ownership
Casio sits in the lower tier
The Casio G-Shock GA-B2100 CasiOak sits at $100–$150 and the Hamilton Khaki Field Automatic at $500–$1,000. On the specs that outlast any price: the G-Shock GA-B2100 CasiOak uses Mineral Glass with About 7 months on a full charge without light; about 18 months in power-saving (Casio), against Sapphire Crystal and 80 Hours on the Khaki Field Automatic. Service intervals are typically 5-7 years for both.
Water Resistance
200m (20 ATM) vs 100m (10 ATM)
The G-Shock GA-B2100 CasiOak is rated to 200m (20 ATM) while the Khaki Field Automatic handles 100m (10 ATM). The G-Shock GA-B2100 CasiOak is better suited for water activities.
Materials Face-Off
| Component | Casio G-Shock GA-B2100 CasiOak | Hamilton Khaki Field Automatic |
|---|---|---|
| Carbon Core Guard (Carbon Fiber-Reinforced Fine Resin) | Casio's proprietary monocoque case technology integrating carbon fibers into fine resin. The carbon fibers dramatically raise the tensile strength and modulus of elasticity of the case structure, allowing the GA-2100 to achieve an 11.8mm thickness — the thinnest analog G-Shock at launch — while maintaining full 10m drop impact resistance. Total case weight: 51g. | Stainless steel, brushed finish. Hamilton does not publish the alloy grade for this reference. |
| Mineral Glass Crystal (Thermally Tempered Silica) | Flat mineral glass with Mohs hardness ~6. Thermally tempered for impact resistance — flexes under force rather than shattering like sapphire. Not scratch-proof, but replacement crystals cost ~$10. | Verneuil-grown sapphire, single-side AR coating. |
| Polyurethane Resin Strap | Durable urethane polymer resistant to sweat, saltwater, UV radiation, and skin oils. Features quick-release spring bars. Known to last 5–10 years with daily wear before degradation. | Super-LumiNova on the hands and hour numerals. Hamilton lists "Super Luminova: Yes" for this reference and does not publish a grade, so none is claimed here. |
| Stainless Steel Caseback (Screw-Down) | Secured by 4 Phillips screws for 200m (20 ATM) water resistance. The GA-B2100 is Tough Solar: a rechargeable cell topped up by any light, so there is no coin cell to swap. Casio rates a full charge at about seven months of normal use without light, and about eighteen months in power-saving. | Full-grain leather (varies by reference). |
| Premium Lineage: Cobarion® & DAT55G Titanium (MRG-B2100) | The luxury MRG-B2100 variant ($3,500+), hand-assembled at Yamagata Casio's Premium Production Line (PPL) by certified "Medalist" craftsmen, uses Cobarion® (cobalt-chromium alloy, 4× harder than pure titanium) bezels and DAT55G titanium (3× harder than pure titanium) bracelet links. | — |
Cost of Ownership Compared
Who Should Pick Which
Pick the Casio G-Shock GA-B2100 CasiOak if…
- Anyone wanting an indestructible daily beater under $100 with serious design credibility
- Water sports enthusiasts — 200m WR with G-Shock shockproofing
- Watch modding enthusiasts — massive aftermarket ecosystem of metal conversion kits
- High-end collectors needing a dedicated beater alongside their luxury pieces
Pick the Hamilton Khaki Field Automatic if…
- Strong value proposition under $1,000 with quality construction
- Active lifestyle wearers — 100m water resistance handles swimming and water sports
- Weekend warriors — 80-hour power reserve means it survives two days off the wrist
- Those who prioritize scratch resistance — sapphire crystal
- Military/field watch enthusiasts who value legibility and durability
Casio G-Shock GA-B2100 CasiOak
- Stealth-black legibility deficit: The GA2100-1A1 has absolutely no Neobrite luminescent paint on hands or indices. Low-light readability is poor — you must rely entirely on the Double LED Super Illuminator.
- Mineral glass scratches: Not sapphire. Daily beater use will accumulate minor scuffs over time. Replacement crystals are cheap (~$10) but require caseback removal.
- Tiny digital subdisplay: The LCD window at 4:30 is small and genuinely difficult to read for anyone with less than perfect vision. The Hand-Shift feature (sweeps hands to 7:35 position to clear the LCD) helps but isn't a substitute for a full digital display.
- Module 5689 is quartz: For mechanical-watch purists, this is a non-starter. For everyone else, it's a feature — better accuracy (±15 sec/month), no winding, no expensive servicing, and solar charging that never needs a battery change.
Hamilton Khaki Field Automatic
- Same H-10 / C07 movement as Tissot PRX and Mido — paying brand premium for the Hamilton heritage
- 3 Hz "slow" seconds beat (visible 6 ticks/sec vs. 8)
- Strap quality is adequate, not exceptional
- No hacking, but movement is auto-only (no hand-wind on the 80h variant — older H-30 caliber refs had it)
Our Verdict
Casio
G-Shock GA-B2100 CasiOak
Choose the Casio G-Shock GA-B2100 CasiOak if you prioritize Casio Quartz (Solar-Powered) engineering, Made in Japan craftsmanship, and 200m (20 ATM) water resistance. At $100–$150, it delivers Quartz Module 5689 (Tough Solar + Bluetooth) with About 7 months on a full charge without light; about 18 months in power-saving (Casio) power reserve.
Check Price on AmazonHamilton
Khaki Field Automatic
Choose the Hamilton Khaki Field Automatic if you value Automatic (ETA C07.611 base) technology, Swiss Made heritage, and 38mm proportions. At $500–$1,000, the Automatic H-10 with 80 Hours power reserve makes it a compelling choice.
Check Price on AmazonThe Bottom Line
The Casio G-Shock GA-B2100 CasiOak and Hamilton Khaki Field Automatic represent two distinct approaches to fine watchmaking — the Casio bringing Made in Japan tradition while Hamilton delivers Swiss Made engineering.
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Our comparisons are generated from a hand-maintained specification database and reviewed under our editorial standards. We use AI tools to assemble pages from that data. We don’t invent specs: every number traces back to the database, and when we correct an entry, the fix is applied site-wide. As an Amazon Associate, The Horologist earns from qualifying purchases.