The crew aboard the USCG-6. Note: Insignia on their helmets. This was unofficial.

USCG-6

U.S. Coast Guardsmen go for a swim under the hull of a famous Japanese landmark in the solomons.  It is the KINUGAWA MARU, beached by the Japanese after being riddled by American gunners.  Ca.  1943-44.  (Coast Guard)
Exact Date Shot Unknown
NARA FILE #:  026-G-2074
WAR &amp; CONFLICT BOOK #:  885

Coast Guardsmen Swim under Japanese Wreck

A newly launched 83-footer, the GC-624 (later 83373 &amp; CG-14 in Rescue Flotilla 1). 
Note the 20mm/80 on deck and the depth charge tracks. Probably taken 1942.