Iirc, the Posse Comitatus applies only to the US Army and it’s offshoot the US Air Force.
The US Coast Guard is routinely used for law enforcement in our recreational rivers, lakes and coastlines.
The USN and USMC aren’t covered by the PC but are covered by directives of the DOD.
Everything you ever wanted to know about:
https://fas.org/sgp/crs/natsec/R42659.pdf
The Posse Comitatus Act and Related Matters:
The Use of the Military to Execute
Civilian Law
Updated November 6, 2018