When U.S. President Donald Trump signed an Aug. 13 national security memorandum aiming to rebuild the United States Navy and America's shipbuilding industrial base, he did more than address a domestic industrial crisis. He set in motion a structural shift in how Washington's premier ally in Northeast Asia will participate in the future of American sea power. For decades, U.S. law drew a hard line around who could build Navy combatants. Restrictions dating back to the Byrnes-Tollefson Amendment kept construction of major naval vessels firmly on American soil, leaving Korea's globally competitive shipyards confined to component supply, maintenance and repair work despite building more commercial tonnage than almost any nation on Earth. The new memorandum does not erase that wall, but it cuts a conditional door through it. Foreign shipbuilders that make "substantial and durable" investments in U.S. yards, either by acquiring a majority stake in an existing American shipyard or building a new one from the ground up, will be temporarily permitted to construct up to two initial vessels at t