The first Ref. 25721ST, also nicknamed "The Beast" due to its staggering proportions, was far ahead of its time. A huge and thick case, measuring approximately 16mm in height. The Royal Oak Offshore Ref. 25721ST starts as D-series. The production of the D-series Audemars Piguet watches start in 1992 already, but the Royal Oak Offshore is delivered to the market in 1993. The first serial number of "The Beast" is D23744 and the last watch is the D97184. The last D-series was produced in 1998. In that time Audemars Piguet produced 1300 reference 25721ST watches in the D-series. All these watches came up in smaller batches (200-100-200-300-200-100-200), adding up to exactly 1300 pieces.

After the first 200 watches, Audemars Piguet started to use the calibre 2226/2840 (instead of the 2126/2840) for the Royal Oak Offshore, which was based on the Jaeger-LeCoultre 889/1 with a Dubois-Depraz chronograph module. Combined with the heavy stainless steel bracelet, the watch weigh approximately 223gr. On the D-series the links of the bracelet have 4 screws - 2 on both sides (on later models that has been reduced to 2 screws- 1 on each side). Besides a very visible gasket below the octagonal bezel, there are also rubber (like) pushers and crown. This material is actually referred to as Therban, a high-performance elastomer that is resistant to extreme temperatures. This material was developed by Bayer in 1975 and marketed as Therban in 1986. The Therban pushers and crown have the same blue tone as the dial.