.The MoD thought these civilian watches were not suitable to the needs of British soldiers, and decided to place an order for custom-built wristwatches. These needed to be accurate, reliable and durable, which in watchmaking terms meant they had to be regulated to chronometer standards, and also be waterproof and shockproof.
The watches also had to have a black dial, Arabic numerals, luminous hour and minute hands, luminous hour markers, a railroad minute track, a shatterproof crystal, and a stainless-steel case. Powering them would be 15-jewel movements, measuring between 11.75 and 13 lignes.
Twelve companies would fulfill this brief: Buren, Cyma, Eterna, Grana, Jaeger-LeCoultre, Lemania, Longines, IWC, Omega, Record, Timor, and Vertex.
https://www.hodinkee.com/articles/dirty-dozen-twelve-military-watches
