The IWC pilots watch was 1st developed in the 1940s for the Luftwaffe. It was called Big Pilots Watch 52 T. S. C. At 55mm it was a large heavy piece designed for military specifications. Delivering the precision of a chronometer and central hacking second enabled pilots to synchronise. These watches had an extra large leather strap so they could be worn externally to a flight suit. The pilots watch evolved in 1948 the mark 11 came out built for the royal air force including a soft iron core.