What happens when a U.S. ship runs out of missiles in the heat of naval battle? How is the rest of a gun line affected if a cruiser has to steam away to resupply its ordnance?

Navy heads have not had to ponder such questions for decades. America’s fleet hasn’t been threatened by a so-called “peer” sea service since a wall divided Berlin and the Soviet navy prowled the seas.

But now, amid a snarling North Korea and heightened tension in the South China Sea, the Navy is planning on bringing back its ability to reload missiles while a ship is at sea.

Chief of Naval Operations Adm. John Richardson told The National Interest of the Navy’s plans during a June interview.

Officials say at-sea reloading is in its earliest planning stages, and analysts believe the move signifies that what was once old in the Navy is now new again.

After the end of the Cold War, Navy brass moved away from preparing a fleet that would have to fight it out on contested seas, according to James Holmes, a professor of strategy at the U.S. Naval War College.

“Naval leadership proclaimed that there was no one left to fight after the Soviet navy,” Holmes said in an email. “The service chiefs basically said America owns the sea.”

But an assertive China and resurgent Russian maritime ambitions are moving Navy leadership back toward conventional warfare tenets.

“We slumbered for twenty-five years after the Cold War,” Holmes wrote in the email. “This is part of getting the kinks out after that long snooze.”

Since the end of the Cold War, ships have been able to rain naval gunfire on Iraq, Afghanistan, Libya, Syria and elsewhere before steaming back to a port for reloading.

But the U.S. would suffer in a conflict with a peer maritime force if ships had to leave the battle to reload, Holmes said.

“The opponent would have weakened our fleet even without scoring a punch,” he said. “If we keep having to rotate cruisers or destroyers back to rear areas to reload, the opponent has subtracted that much combat power from the fleet.”

Holmes said the end of at-sea reloading after the Cold War was part of a larger loss of hardware and tactics designed to fight peer opponents.

“At-sea reloading of missiles is one of those capabilities that needs rejuvenating,” he said.

Exactly how the Navy will reload the MK 41 vertical launch system currently in use on most cruisers and destroyers remains to be seen.

It wasn’t an easy proposition in the past, according to Eric Wertheim, a naval analyst and author of “Combat Fleets of the World.”

“Imagine a revolver, think of how long it takes to do the single bullets,” Wertheim said. “They’re not speed loaders.”

Cranes were installed on the earliest cruisers in the 1980s to assist with reloading, but it remained time-consuming and perilous.

“It’s stressful for the equipment, it’s stressful for the people and it’s a challenge that’s been looked at for many years,” Wertheim said. “It was very hard to do, and it was not very practicable, so when the need for it diminished, it just fell by the wayside.”

Unlike ammunition, fuel or stores, missiles can’t be replenished while underway.

Any reloading during choppy seas could also damage a vertical launch system cell, Holmes said.

One workaround could involve reloading near Pacific islands and atolls off of expeditionary transfer dock ships like the John Glenn or Montford Point, he said.

“A cruiser or destroyer might meet up with an ammunition ship or converted merchantman, using the island’s lee to block out the wind and seas,” Holmes said. “That would let us rearm quickly and without damage.”

However it’s done, plans to bring back at-sea reloading in 2017 reflect an evolving world.

“Only now are we starting to take the Chinas and Russias of the world seriously,” Holmes said. “Rearming wasn’t a high priority if there was no foe to fight.”