1971 Fortis Marinemaster ref. 8001 chronograph.
39mm. case and 20mm. lug width. Yellow sub dials and magenta-colored hands. This watch was also produced in a version with blue sub dials.
The movement employed is the 17-jewel, manual wind Valjoux 72. Interestingly, Fortis reissued the watch in 2014 as a limited edition, but with an automatic movement.
The Valjoux 72 is a three register column wheel manual wind chronograph movement which traces its origins back to the 1930s. The V72 was used in the Daytona Paul Newman and many other high end watches, but also in some lesser known brands; expect to pay a premium price for watches with this rare and celebrated movement.
Alone, it is worth more them US$500, often used as spare parts for more expensive watches, and I go further, an unmarked Valjoux 72 can be signed and turned into a Rolex, Breitling, Heuer, Jaeger and others, so be careful with identification.