The Earth Mars Coalition Navy, abbreviated EMCN, is the joint naval taskforce of Earth (the United Nations Navy) and Mars (the Martian Congressional Republic Navy). It has policed the Sol system together for almost a century. According to Dimitri Havelock, the EMCN has about a hundred gunships at its disposal at the time the Eros incident took place.
Since the events of Leviathan Wakes, Earth and Mars have been in a state of war, sometimes hot, sometimes cold; as such, EMCN forces are now divided into the UN Navy and the MCRN. (The exception to this division is any action involving the Belt or Outer Planets - the Inner Planets cannot afford to look weak to the Outer Planets Alliance.)