According to WP, a total of 6 Martin Mars were built: The first Hawaii Mars
(lost 1947), the Marianas Mars (lost 1961), the Philippine Mars (with
Coulson), the Marshall Mars (lost 1950), the Caroline Mars (lost 1962), and
the second Hawaii Mars (with Coulson, the one photographed).

So a total of two out of six survive, both working as firebombers for
Coulson Flying Tankers.

MH.