A photograph of United States Marines arriving in Innsmouth, Massachusetts on February 5th, 1928. Additional troops were brought in once the sheer number of prisoners captured during the February 3rd raid, and the necessity of moving them across country by train, became clear. Three coastal auxiliaries were used to shuttle in the relatively small contingent available from Norfolk to the Innsmouth pier. Those units accompanied naval military police and United States Marshals on the train ride to the prisoners' final internment facility.
This is a totally unretouched photograph from December of 1921 of troops offloading at the Marine Flying Field in Quantico, Virginia. In the real world, by 1928 the Marine contingent at Norfolk was an officer-heavy training command with just a few hundred men. Given the nature of the Innsmouth detainees it seems likely that guard duties for the train trip inland would have fallen on naval personnel, a few special agents from the Department of Justice, and US Marshals out of the Boston office.