14 U.S.C. § 103: Department in which the Coast Guard operates

The Coast Guard shall be a service in the Department of Homeland Security, except when operating as a service in the Navy. Upon the declaration of war if Congress so directs in the declaration or when the President directs, the Coast Guard shall operate as a service in the Navy, and shall so continue until the President, by Executive order, transfers the Coast Guard back to the Department of Homeland Security. While operating as a service in the Navy, the Coast Guard shall be subject to the orders of the Secretary of the Navy, who may order changes in Coast Guard operations to render them uniform, to the extent such Secretary deems advisable, with Navy operations. applicable appropriations of the Navy Department shall be available for the expense of the Coast Guard; applicable appropriations of the Coast Guard shall be available for transfer to the Navy Department; precedence between commissioned officers of corresponding grades in the Coast Guard and the Navy shall be determined by the date of rank stated by their commissions in those grades; personnel of the Coast Guard shall be eligible to receive gratuities, medals, and other insignia of honor on the same basis as personnel in the naval service or serving in any capacity with the Navy; and the Secretary may place on furlough any officer of the Coast Guard and officers on furlough shall receive one half of the pay to which they would be entitled if on leave of absence, but officers of the Coast Guard Reserve shall not be so placed on furlough.