Starting in 1904, IWC also produced a pocket watch with a particularly unusual movement — Calibre 71 and, for Savonette models, Calibre 72. Unlike IWC’s typical movements with three-quarter plates or finger-bridges, these movements had curved bridges and cocks that were almost lyrical in design. These movements are called “fishtail” because of their curved cocks, looking like fishtails.
The Calibre 71 and 72 movements were mostly produced with 16 jewels, a Breguet hairspring and with fine adjustment. They were 19 ligne (approximately 42.86mm) in diameter and with a height of 6.5 mm (in 1904) or 6 mm (in 1917).
Many collectors consider them among the most beautiful movements ever produced, but only 600 of each movement were made from 1904 until 1917, plus an additional 12 produced in 1923. These last 12 were made with 21 jewels and were observatory-rated in Neuchatel as Class I.
All IWC Calibre 71 and 72 watches are highly collectible, especially the Calibre 71 watches produced in 1917 in only 180 examples for the British Royal Navy.