US marines are the designated guards for US embassies because they are under the executive branch and hence represent the US government historically.
Marines were also the only branch that could be deployed at the orders of the Executive branch(President and Cabinet) and in essense did not require congressional approval until the war powers act.
Marines were also the only branch that could be deployed at the orders of the Executive branch(President and Cabinet) and in essense did not require congressional approval until the war powers act.