This watch is accompanied by a Patek Philippe Extract from the Archives confirming production in 1944 and its subsequent sale on July 8th, 1946.
Patek Philippe produced a total of 281 examples of reference 1518, beginning in 1941. It was later replaced by the reference 2499, also a perpetual calendar chronograph, but with a wider diameter and fluted lugs.
A similar example of reference 1518 is illustrated in Patek Philippe Wristwatches by Martin Huber & Alan Banbery, 2nd edition, pp. 303.