"All major warships were constantly under one of three 'conditions' while at sea. These were either X-Ray, Yoke, or Zebra. Condition X-Ray was the most favorable. It meant that the ship was cruising under normal conditions with no expectation of any damage. In this case little attention was paid to keeping watertight doors shut, and there was plenty of ventilation to berthing quarters belowdecks. Condition Zebra was the final extremity when a ship was buttoned up for battle with almost every single compartment and passageway shut off from another by watertight steel doors with hatches and scuttles dogged down hard and fast.
"Condition Yoke, however, was quite another story. Halfway between the cruising condition of X-Ray and the general quarters condition of Zebra there were conditions Yoke and Yoke Modified. Yoke, itself, in the jargon of the Navy simply means that the ship is in waters where an attack or accident might and even probably will occur, but Condition Yoke Modified was a somewhat hypothetical situation that existed more in the mind than in the realm of cold hard facts. Officers and men alike knew that they could not sleep in superheated compartments—spaces that were mechanically heated by boilers and firerooms or from the blistering tropical sun....
"So, Condition Yoke Modified meant that on the night of July 29 the Indianapolis was steaming westward across the Pacific in about the same condition of watertight integrity as she would have fifteen or twenty years earlier when the only potential hazard was a derelict ship or an unexpected storm.... This was not an oversight on the part of officers or leading petty officers. It was simply standard procedure for all overaged warships still plodding about the Pacific in the final days of the war."
—Thomas Helm, Ordeal by Sea: The Tragedy of the U.S.S. Indianapolis, 1963 (New York: Signet, 2001), 24–25