It's the 40th anniversary of the first ever G-Shock watch, and Casio is celebrating by releasing a new version of the original timepiece in hardened steel, making it tough enough for outdoor adventures.

As Casio fan site G-Central reports, the new Recrystallized Series includes three colorways, and is inspired by the classic DW-5000C-1A from 1983.

The gold GMW-B5000PG-9 and silver 聽GMW-B5000PS-1 are made using a stainless steel recrystallizing and deep hardening process. Carbon is infused into the surface of the steel, resulting in a tougher finish than simply adding a coating.

The process also gives the metal an unusual look, which resembles flakes and is subtly different in every watch.

Both these watches also offer solar charging, 200 meter water resistance, and Bluetooth support. This allows them to connect to the Casio Watches smartphone app, which you can use to select time zones, adjust watch settings, and set reminders.

Casio has also launched the DW-5040PG-1, which takes the same design cues from the original G-Shock, but is made with a black resin bezel and band made using biomass plastics to reduce reliance on virgin plastics.

Casio has yet to announce prices for the new limited edition watches, but they are due to go on sale in April.