David McCallum wears a stainless steel Ulysse Nardin 1846 Marine Chronometer with white dial on the tv series NCIS. We don't have a good screenshot that shows the watch, but a source at NCIS has confirmed McCallum wears this watch on the set of the popular series. The few images we could find seem to support the claim. On one of the photos, the little Ulysse logo on the metal band can just be spotted. It's not certain if the model worn by McCallum has Roman or Arabic numerals.

Read a review of the 1846 Marine Chronometer on timezone.com.

Ulysse Nardin watches are quite rare and hard to find at only a select group of retailers. Online you can usually find some Marine Chronometers on eBay.