The Chain Forge at Charlestown Navy Yard: Anchor Chain for the Navy's Largest Ships

Workers named the big steam drop hammers in Building 105, the chain forge of the Charlestown Navy Yard in Boston: Big Barney, Old Harry, Little Andy and the Mighty Monarch. Like a blacksmith's hammer, only weighing up to 25,000 pounds, they pounded hot metal into shapes far too big to forge by hand — above all, links of anchor chain.

A forge for a growing Navy

Building 105 under construction in 1902, with the smokestack of its own power plant. Boston National Historical Park, BOSTS 9643-105-9a.

By the 1880s, Charlestown was already the Navy's main maker of anchors and anchor chain. Building 105, finished in the first years of the 1900s, was built for the fast-growing size and number of ships: a steel frame against fire, room for heavy hammers, and its own boilers and power plant, which for a time also powered the yard's new cranes and dry dock pumps.

Output was still slow. Anchor chain was wrought iron, each link welded by hand, and in World War I the new ships needed far more than the forge could make. Cast steel chain — molten steel poured into molds — proved stronger, faster and cheaper, and became the Navy standard in 1921. Building 105 had no casting equipment, and the Navy chose not to convert it. The forge faced obsolescence.

Finished chain from Building 105, in lengths called shots, joined by detachable links also designed at the yard. Boston National Historical Park, BOSTS 10103-1181.

The die-lock link

Master Blacksmith Albert Leahy, Leading Blacksmith James Reid and Mechanical Engineer Carlton G. Lutts designed a chain the forge's hammers could make. Their die-lock link needed no welding:

• Each link has two halves: a stem with a toothed peg and a socket with a matching hole.
• The socket half is heated to 2,100°F so it expands just enough to take the cool stem.
• The hammer then strikes several times, locking the two into one link.

The two halves of a die-lock link. Historic American Engineering Record, 2013.

The steel die-lock chain was stronger than wrought iron — and stronger than cast chain. First used on a ship in 1926, it became the standard for the entire fleet in 1928, and Charlestown was again the Navy's chief chain maker. In World War II, orders were so heavy that smaller chain went to private firms, but nearly every aircraft carrier, battleship and cruiser carried chain from Building 105 — as has nearly every Navy carrier since.

The 4¾-inch chain

Chain is sized by the thickness of the bar in each link, not its length. The biggest Building 105 made was 4¾-inch chain — every link 4¾ inches thick and 360 pounds — developed in the 1950s for the new Forrestal-class supercarriers. Congress considered closing the forge and the yard's ropewalk to stop the government competing with industry, but no private company bid on the big chain, so the work stayed in Charlestown.

Bigger chain meant bigger tools. In 1952 the Navy installed the 25,000-pound Monarch hammer, paved the shop's last dirt floor — a blacksmith's tradition that eased the strain of hammering, now in the way of forklifts — and finally added proper ventilation to a shop that filled with smoke and topped 100 degrees on summer afternoons.

Each new link is forged white-hot onto the end of the chain, one at a time, January 1967. Boston National Historical Park, BOSTS 15908-18.

Still at sea

Charlestown is the only place in the world that has made 4¾-inch die-lock chain. When the Navy closed the yard in 1974, it had no other source, so it reuses the old chain: when a carrier is retired, its chain moves to a new one. Chain forged in Building 105 still hangs from Nimitz-class carriers some 50 years later.

Sources

Based on "Charlestown Navy Yard: Chain Forge," Boston National Historical Park, National Park Service; a work of the United States government in the public domain. It draws on the park's 2012 Historic Structure Report for Building 105, the Historic American Engineering Record (HAER No. MA-90-3), a 2014 special resource study of the forge machinery and a 1980 National Research Council report. The source is inconsistent in places: it gives Building 105's completion as 1904 in the text and 1905 in a caption; it says the Monarch hammer came twenty years after Big Barney (1936) but was installed in 1952; and it gives a shot of chain as 90 feet in one caption and 60 feet in another. An illustration from a 1938 Erie Foundry trade catalog is not reproduced.