The US Marine Corps does NOT have Medics. So that branch of service cannot be allowed. Marine Corps medics aka "Devil Docs" are provided by the US Navy.
Also noted US Navy Ranks are not included: Those can be found easily by doing an internet search.
Minimum Rank to join Navy Seals is E-3 (Seaman) though most likely will be E-4 (Petty Officer 3rd Class) PO3 or above.
D.Merrill (L/Cpl USMC)