Fortis Military Chronograph, Venus 150, clamshell brevet 189190

Fortis Military Chronograph – Venus 150 – Clamshell Case

A beautifully preserved vintage Fortis chronograph featuring an exceptional tropical gilt dial that shifts from deep black to rich chocolate brown depending on the light. The warm patina and glossy gilt printing give it tremendous character and classic military-era presence. Combined with the rugged clamshell waterproof case and the legendary Venus 150 chronograph movement, this is a highly charismatic and historically important piece.

Specifications
Manual wind chronograph
Venus caliber 150
Rare waterproof “Clamshell” case
Brevet (patent) 189190
Case size: 34.5mm excluding crown
Lug-to-lug: 42mm
Two-register chronograph layout
Tachymeter and telemeter scales
Beautiful gilt dial with tropical undertones

The Clamshell Case

The Clamshell case, protected under Swiss Patent No. 189190 (filed in 1936 and granted in 1937), was developed by the renowned case maker Schmitz Frères and later licensed to Gallet. Widely regarded as one of the most innovative early waterproof watch case constructions, the Clamshell represented a major technical breakthrough in the evolution of wrist chronographs.

Its ingenious design employed four external screws positioned through the lugs, compressing the case back, middle case, and crystal assembly into a tightly sealed unit. This system created one of the first genuinely waterproof chronograph cases at a time when most watches remained highly vulnerable to moisture and dust intrusion.

These cases were widely used by military and tool-watch manufacturers because of their durability and practical waterproofing during the pre- and post-war periods. Today, original clamshell chronographs are highly sought after by collectors due to their technical significance, rarity, and unmistakable vintage aesthetic.

About Fortis

Founded in 1912, Fortis is one of the oldest continuously operating Swiss watch manufacturers. The brand became known early on for producing robust and reliable tool watches and was among the pioneers of automatic wristwatches through collaboration with English inventor John Harwood in the 1920s.

Fortis later gained international recognition for aviation and military watches and eventually became closely associated with space exploration, supplying watches for Russian cosmonauts and space missions. Vintage Fortis chronographs from the 1940s–1950s are especially appreciated today for their honest military styling, excellent movements, and strong historical character.

Overall Impression

This example perfectly captures the appeal of early military chronographs: compact proportions, technical innovation, and incredible dial character. The gilt dial is unquestionably the highlight, showing remarkable depth and warmth depending on viewing angle and lighting conditions. Paired with the rugged clamshell construction and reliable Venus movement