The “new” Alpina Seastrong Diver 300 in recent hands-on coverage is the green, no-date Seastrong Diver 300 Heritage, reference AL-520GR4H6. Its defining update is the green sunray dial and matching rubber strap—not a new 2026 launch established by the available coverage. Alpina lists a 42 mm steel case, 300 m water-resistance rating and automatic AL-520 movement with a 38-hour power reserve. The specifications below are manufacturer claims; on-wrist impressions are attributed to the reviewer who wore it.
What is new about the green Seastrong Diver 300 Heritage?
Horologii’s Louis Howson described the green Heritage as a new color execution in a hands-on article published June 8, 2025. The watch is reference AL-520GR4H6, with a green sunray dial and green rubber strap. “New” here refers to that 2025 coverage of the color variant; the available information does not establish a 2026 launch.
Howson’s article provides the published on-wrist impressions of this particular green model. Those impressions belong to Howson, rather than to an independent test reported here. No independent timing, water-resistance, lume, comfort or finishing test is established by the product specifications.
AL-520GR4H6 specifications
Alpina’s US and UK product pages identify this as a time-only Heritage model. The listed specifications are:
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#1 Best Overall
- Water-resistant to 300M, this 42mm Seastrong Diver 300 Heritage Automatic with steel case lets you measure your immersion time in hours, minutes and seconds. Its black lacquered sunray-brushed dial features gold plated luminescent hands, making it easy to read, even in the low light of the deep sea. Featuring a modern automatic caliber with 38 hours power reserve and an anti-scratch sapphire glass. Comes with two straps, one in brown calfskin leather and the other in beige topstitched rubber.
- Hours, Minutes, Seconds
- Silver-Tone Stainless Steel
- Anti-Reflective Sapphire Crystal
- 30 Meters and 3 Year Limited Warranty
- Case: 42 mm stainless steel; 12.3 mm thick.
- Water resistance: 300 m / 30 bar, as specified by Alpina.
- Crystal: anti-reflective sapphire.
- Dial and strap: green sunray dial and green rubber strap.
- Display: hours, minutes and seconds, with no date.
- Timing scale: an internal 60-minute immersion-time scale.
- Movement: automatic AL-520; Alpina UK identifies it as based on the Sellita SW200, with 26 jewels and a frequency of 28,800 alternations per hour.
- Power reserve: 38 hours, according to Alpina.
- Strap width: 21 mm.
The 300 m rating and elapsed-time scale are manufacturer specifications, not evidence of an independently conducted dive or water-resistance test. They should not be read as a certification claim.
What the hands-on coverage says—and what it does not
Howson’s June 8, 2025 Horologii article is the hands-on source for the green variant: Horologii. Its wrist impressions can help readers understand how the watch was experienced by that reviewer, but they are not a substitute for trying the watch on personally. The product pages establish dimensions and materials, not how the watch will fit a particular wrist.
Rank #2
- The Seastrong Heritage model is inspired by the 1960’s professional diver design, a beautiful re-issue of this historic model. This timepiece features an automatic movement with a 60-minute internal rotating bezel. It also has a textured rubber strap, vintage white and black dial, screw down crown and an engraved caseback to protect the movement from everyday elements.
- 300M water resistant with uni-directional turning 60m diving bezel
- AL-525 Caliber - Automatic Self-wind Movement, 26 jewels, 38 Hours Power Reserve
- 42mm Case Diameter with Polished Stainless Steel Case
- Scratch Resistant Sapphire Crystal
Monochrome’s hands-on coverage concerns a separate black-and-gilt Heritage reference, AL-520BY4H6. It reports that variant’s 42 mm by 12.3 mm case, AL-520 movement based on the SW200, 38-hour reserve and an additional rubber strap alongside its leather strap. Those details are not a firsthand assessment of the green AL-520GR4H6.
Do not confuse the green no-date model with the date version
The Seastrong Diver 300 Heritage name covers distinct configurations. In particular, the silver-and-black AL-525S4H6 is the date-equipped model, with a date at 4 o’clock, an AL-525 movement and a black rubber strap. Those features do not belong to the green AL-520GR4H6.
Rank #3
- The Alpina Seastrong Diver 300 Heritage is the ultimate automatic dive watch, water resistant to 300M and measuring immersion time up to 60 minutes.
- The 42mm stainless steel case features a green sunray dial with luminous silver colored hands.
- The stainless steel caseback is engraved with Alpinas beloved Alps and a trident, and is anchored to a green rubber strap that is sand, sea salt- and corrosion-resistant.
- Equipped with the AL-520 automatic caliber with 38hr power reserve.
| Reference | Dial and strap | Movement and display | Price or availability stated by Alpina |
|---|---|---|---|
| AL-520GR4H6 | Green sunray dial; green rubber strap | AL-520 automatic; time only, no date | US page listed $1,995; UK page listed £1,495 and showed “Coming Soon” when accessed |
| AL-525S4H6 | Silver/black dial; black rubber strap | AL-525; date at 4 o’clock | UK page listed £1,595 and showed “Coming Soon” when accessed |
| AL-520BY4H6 | Black sunray dial with gold-color indexes and hands; brown calf-leather strap plus additional black rubber strap | AL-520; no date | Not stated in the cited product information |
The prices and stock labels above are regional page states recorded when accessed, not guaranteed current prices or availability. The black-and-gilt reference is included to clarify the range, not as a price comparison.
Price and availability: check the reference and region
Alpina’s US product page for AL-520GR4H6 displayed $1,995 when accessed; the UK page for the same reference listed £1,495 and displayed “Coming Soon.” Because the pages show different regional pricing and stock signals, check Alpina’s listing for your market and the exact reference before making a purchase decision. The UK page for the distinct date model AL-525S4H6 listed £1,595 and also showed “Coming Soon” when accessed.
Rank #4
- The Seastrong Diver Extreme Automatic is housed in a 39 x 40.50mm steele case and features three central hand-polished hands that sit at the heart of a dial textured with Alpina's iconic triangular emblem, punctuated by a date window at 6 o'clock.
- For maximum readability, both the hours and minutes hands and the hour markers have been coated with luminous material and the date window features black figures on a white background.
- WR to 300m, and comes on a bright orange rubber strap.
Is the green Seastrong the right configuration?
- Choose the green AL-520GR4H6 if you want the green dial and rubber strap with a clean, no-date display.
- Consider the AL-525S4H6 if a date display is important; it is a different movement and configuration.
- Compare the AL-520BY4H6 if you prefer the black-and-gilt look and the leather-plus-rubber strap arrangement described for that variant.
- Check before changing straps: Alpina specifies a 21 mm strap width for the green model, but width alone does not establish that an aftermarket strap will fit its attachment or end shape.
Alpina’s 2024 Diver Extreme Automatic is a separate collection. Its external-bezel and ceramic-insert details should not be transferred to the Heritage, whose listed timing scale is internal.
Quick Recap
Best Value
- Hour, Minute, Second, Date
- Anti-Reflective Sapphire Crystal
- Black Rubber Strap
- 300MM Water Resistant
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
