Production of the Mark XI, one of the most legendary navigator's watches, was launched in 1948. The model was always fitted with an IWC calibre 89, with or without the hacking feature, and cased in stainless steel, some early versions in chrome-plated brass.
It was issued to the British Ministry of Defence and used by the RAF as well as Commonwealth forces, including South Africa, New Zealand and Australia. The engraved numbers on the back differ depending on service. Dials and military markings also vary but those for military use show a broad arrow, some also the Ministry of Defence specification for tritium, the encircled T.
The present watch is engraved with Mark XI reference number 6B/346, the "6B" signifying "Flying", the combination of "6B/346" was the watch specification. Number 158 is the serial number and 50 the year of production.
The model is illustrated in Ore d'Oro 2 by Jader Barracca, Giampiero Negretti, Franco Nencini, p. 207.