In fact, Corpsmen are navy soldiers (see http://en.wikipedia.org/wiki/United_States_Navy_Hospital_Corpsman) but some are assigned to USMC units. When they are with USMC, they wear the same uniform than USMC ; so the current marpat woodland and desert uniform. But they usualy change the branch tape and have their own US Navy branch tape and ranks :

(US Navy ranks pinned)


(US Navy name tape and corpsman badge embroidery on name tape)
(note the US Navy branch tape and the cap without EGA !)


And there's another difference between US Navy Corpsmen and USMC marines - their garrison cover ! The USMC garrison hat have an EGA embroidery on it. The ones of US Navy Corpsmen doesn't have the EGA, but they pinned their own USN rank ;




For comparison, here's one of the USMC (with EGA embroidery) :




And last one in woodland marpat :






(US Navy ranks pinned)


(US Navy name tape and corpsman badge embroidery on name tape)
(note the US Navy branch tape and the cap without EGA !)


And there's another difference between US Navy Corpsmen and USMC marines - their garrison cover ! The USMC garrison hat have an EGA embroidery on it. The ones of US Navy Corpsmen doesn't have the EGA, but they pinned their own USN rank ;




For comparison, here's one of the USMC (with EGA embroidery) :




And last one in woodland marpat :










