Round Four of the Battle of the Branches sets sail as four Naval officers must forge a multipurpose Naval Mark 3 Dive Knife with metal from a giant anchor chain. It's sink or swim as delaminations and forge weld failures plague some of the bladesmiths. After a particularly brutal round of testing, two sailors return home to recreate the intricate and iconic Naval Officer's Sword. Which smith will secure a spot at the Navy Anvil, a chance at glory, and the $50,000 grand prize?