Correction: A previous version of this story mischaracterized the growth of work for the industrial base moving from the Block IV to Block V Virginia-class submarine design. The 750,000 and 1 million man-hour figures refer only to work that was previously done at the submarine construction yards that is now offloaded to vendors. WASHINGTON — This fiscal year was expected to be the first in which the U.S. Navy dipped into a “trough” in its submarine force, falling below the previous requirement