Created only as a prototype in 1943 and intended for deck officers, the Mare Nostrum chronograph has now become a reality. Distinguished by its wide milled crown and push buttons in the 1940s style, it also has a very strong case (needing over 40 manufacturing operations) made from a single block of AICI 316L stainless steel.

Side view of the White dial Mare Nostrum

This version offered released in 1997 has a modified bezel and dial and a limited edition of only 400 watches. 

Extract from Panerai Brochure

There are basically three dial variation but I am listing the White dial. The dial recalls the exclusive Panerai design with large Arabic numberals and baton hands, while also accommodating dials for small seconds and minute counter. It differs from the 1993 version in having a narrower bezel and a minute scale outside the hour markers rather than within them. With a diameter of 42mm, the watch-resistance is guaranteed to a depth of 50 meters (164 feet), but Panerai has tested it to a pressure equivalent to 70 meters (230 feet).

View from the front

In order to resist this pressure the push buttons are inserted into the case through special sleeves with double sealing rings. 

Scanned from Panerai brochure - Robust case

The case is obtained from a single block of steel and requires more than 40 processes before it is finished. Stringent tests are made to ensure that is is hermetically sealed.

Scanned from Panerai brochure - Movement with 41 jewels

The sapphire glass is flat and the tachymeter scale for measuring average speeds is engraved on the identification numbers and data concerning the maximum operating pressure are engraved on the screw back. The hand-wound mechanical movement is a high quality 11 1/2-lign Swiss calibre with 41 jewels. The Glucydur balance making 28,800 alternations per hour is fitted with an Incabloc anti-shock system and a micrometer regulator.

View from the back of the case

The bridges and plates are hand-finished with cotes de Geneve decoration, while the movement is adjusted in four positions, ensuring a daily accuracy of 0+10 seconds. The main components are made of non-magnetic alloys which are also insensitive to variations of temperature.

Beautiful original strap with large buckle. The earlier design of Panerai has huge buckle

Brand : Panerai "Mare Nostrum" Chronograph in Steel
Item : PAM00007-Panerai
Reference : OP6501
Movement : Manual Mechanical
Year : 1999
Gender : Gents
Dimension : 42 x 53mm

Close-up of the huge buckle from Panerai earlier design. The earlier design of Marina Luminor has this huge buckle too!

Remarks

This is a Limited edition of 400pcs. Most collectors missed this model in 1997 when Panerai was still new then. This design was actually an original design dating back to 1940s. Sapphire crystal with engraved bezel. Brand new condition.