He also received instruction in ordnance at the Washington Navy Yard in Washington, D.C., worked in the Navy Hydrographic Office, completed the course of instruction at the Naval Torpedo Station at Newport, Rhode Island, and attended the Naval War College at Newport.

During the Spanish–American War in 1898, Rush served as a turret division commander in the armored cruiser USS Brooklyn, the flagship of Rear Admiral Winfield S. Schley's Flying Squadron during blockade operations off Cienfuegos, Cuba, and participated in the Battle of Santiago de Cuba on July 3, 1898.

Detached from Brooklyn in October 1899, Rush went to sea in the battleship USS Massachusetts (BB-2) as executive officer.

In the ensuing years, Rush again alternated tours of duty afloat with assignments ashore.

His citation took note of the fact that he was required to be at points of great danger in directing the officers and men of the brigade and that in doing so he exhibited "conspicuous courage, coolness, and skill."

Rush took command of the Boston Navy Yard on November 6, 1914, a post he held until he requested retirement on October 9, 1916.

His duties required him to be at points of great danger in directing his officers and men, and he exhibited conspicuous courage, coolness and skill in his conduct of the fighting.