On December 7, 1941, a battleship still carried on Japanese naval books as “Battleship No. 1” fired nine shells from her 18-inch guns across 32. 5 kilometers. That ship, later named Yamato, was built to a width of 127 feet—so broad she could not fit through the Panama Canal, which had locks only 110 feet wide.
The design was deliberate: Japanese planners wanted any American battleship built to fight her to be too wide to move between oceans. The specifications began in October 1934, when Japan’s Naval General Staff asked the Bureau of Naval Construction to study a new battleship armed with 18-inch guns. Captain Kitaro Matsumoto, a naval architect involved from the first drawing, later explained the reasoning in the U. S.
Naval Institute’s Proceedings in 1953. Japan could not match American shipyards ship for ship, so each new Japanese vessel had to be formidable enough that the U. S. could not counter it for years.
The second requirement was tied to the canal: planners wanted a ship so large that whatever Washington built to fight her could not pass from one ocean to the other. They judged it unlikely that even the U. S. would fund two full battle fleets, one for each coast.
Working from the other direction, Japanese designers calculated that the largest battleship the canal locks could pass would displace about 63,000 tons, make 23 knots or less, and carry ten 16-inch guns. Every design choice was made to beat that reference. The guns were set at 18 inches because a ship limited by the locks would be limited to 16. The armor belt was specified at 16 inches of steel, enough to stop an 18-inch shell fired from beyond 20 kilometers.
The hull was made wide enough to carry that armor above twelve boilers arranged in four rows of three, an arrangement Matsumoto said only a ship of that breadth could hold. The first design drawing, completed in March 1935, came out at 294 meters long and 41. 2 meters wide, with a top speed of 31 knots. The naval staff found that too large, so the designers gave up some speed, settling for about 27 knots—a significant concession for a navy that had long prized speed.
By the summer of 1936, the dimensions were nearly final, with steam turbines paired with large diesel engines for range. Two months later, however, a basic fault was discovered in the same class of diesel already installed in three submarine tenders. Since the new ship’s engine rooms would sit under 8 inches of armor, nothing installed beneath that deck could ever be removed for repair. The designers dropped the diesels, installed turbines of 150,000 shaft horsepower, and completed the final drawing in March 1937.
It was the 23rd. Before the shape was fixed, the navy towed 50 hull models through its largest test tank in Tokyo. One result was a bulbous bow so large that it cut resistance by 8. 2 percent at 27 knots.
On her full-power trial, Yamato made 27. 5 knots. Shifting from the design to construction, the navy rebuilt its yards to fit the drawing. At the Kure Arsenal, workers deepened the building dock by about a meter so the finished hull could float and raised the gantry crane to 100 tons capacity to swing armor plate.
They also roofed over the far quarter of the dock because a nearby hill looked straight down into it. Battleship No. 1’s keel was laid there on November 4, 1937. The armor required its own plant.
About $10 million went into new mills, and a single side plate could weigh 68. 5 tons, nearly 20 feet long and 16 inches thick. At the Mitsubishi yard in Nagasaki, the second ship was to be launched from a slipway at a launching weight of more than 35,000 tons. Mitsubishi strengthened the ways, added almost 60 acres of workshops, and built floating cranes rated at 350 and 150 tons to handle armor and gun fittings.
Yokosuka and Kure each received new dry docks for additional ships. The guns presented a problem no single yard could solve. Every one of the 18-inch weapons was manufactured at Kure, where gun production had long been concentrated. A single turret with its three guns weighed 2,774 tons—as much as a large destroyer—and the parts could reach Nagasaki or Yokosuka only in a ship built for that purpose.
So the Navy built one. She was the Kashino, laid down at Nagasaki in July 1939 and registered on paper as an “auxiliary turret conveyance warship. ” In October 1941, she brought the first of the second ship’s big guns and a turret up from Kure, and the yard’s big floating crane swung them aboard. The yard covered them in canvas the moment they touched the deck.
Secrecy was treated as part of the same effort. In every paper, the 18-inch gun was called the “special type 40 cm,” a name that made it sound like a 16-inch weapon, while the actual bore was 46 centimeters. At Nagasaki, the slipway was hidden behind a curtain of fiber rope so large that fishermen in Kyushu reportedly ran short of it. The afternoon before the second ship was launched, the yard shut its gates without warning and cut communications with the outside.
Workers learned the launching hour that day and worked through the night. She slid into the water at 8:55 on the morning of November 1, 1940, in front of a few dozen senior officers, while about 1,800 police, military police, and sailors kept the town away from the water. As soon as she was afloat, tugs brought a passenger liner, the Kasuga Maru, alongside her to disguise her outline. She was named Musashi that morning, though most official papers continued to call her “Warship No.
2” until she joined the fleet. The machine also worked on the people it was built to deceive. In January 1938, the American naval attaché in Tokyo, Captain Harold Bemis, reported that Japan was building two 16-inch-gun battleships, considerably heavier than the old treaty limit. The British, German, and French attachés put the figure at 45,000 tons.
The Soviet attaché concluded Japan could not cast guns that large at all without buying machinery abroad. As late as October 1942, the Office of Naval Intelligence estimated the ships at 35,000 tons with nine 16-inch guns. In February 1944, American reconnaissance aircraft photographed the fleet anchorage at Truk, and one frame caught one of the big ships in a corner. Photo interpreters called her guns 18 inches, and ship design experts who were brought in to check agreed she likely displaced at least 60,000 tons.
Then the same experts argued against their own figures and called such a ship impractical on grounds of stowage, propulsion, docking, and navigation—even as the ship sat in their photograph. Historian John Prados, in his account of American codebreaking against the Japanese Navy, describes what finally shifted the estimate. In June 1944, a prisoner taken on Saipan, a former yeoman to Admiral Yamamoto, repeated the jokes Japanese sailors told about their “special type 16-inch” guns. Edwin Layton, the Pacific Fleet intelligence officer and until then a firm believer in 16-inch guns, gave up the smaller figure.
Yet the intelligence weekly in Washington was still printing 40,000 tons at the end of August 1944. The Japanese rule had been built against a real constraint. Since the canal opened, American battleships had been drawn to fit its locks: 110 feet wide with a thousand feet of usable length. The North Carolina and South Dakota classes came out about 2 feet narrower than the chambers.
The Iowa class, faster still, kept that beam and found speed in a longer hull. But the rule could move. On August 11, 1939, Congress authorized a third set of locks, 30 feet wider than the old ones, at a cost put at $277 million. Dredges started on the Pacific approach on July 1, 1940.
Eighteen days later, the Two-Ocean Navy Act authorized five battleships of the Montana class, each 121 feet wide—too wide for the old locks, on the understanding that wider ones were coming. The assumption in Tokyo had been poured into armor that could never be altered, but the country that assumption described was still free to change its mind. Neither the ships nor the new locks were finished. The Navy suspended the Montana class in May 1942 before a single keel was laid, when carriers, anti-submarine ships, and landing craft took priority for steel.
On May 23 of that month, the Secretary of War stopped the canal excavation with almost 13 million cubic yards already removed, and the Montana class was cancelled in July 1943. The machine’s products went to war on their own schedules. On December 1, 1941, the auxiliary ship Kashino’s callsign was changed to JGMQ. The Navy decided in June 1942 to complete the third ship of the class as an aircraft carrier.
With no more turrets to carry, the Kashino’s holds were covered over, and she was used to haul ammunition and stores. On September 4, 1942, 70 nautical miles northeast of Kaohsiung on Formosa, the submarine USS Growler, under Lieutenant Commander Howard Gilmore, put two torpedoes into her. She settled by the head with her screws out of the water but stayed afloat. Gilmore opened fire with his deck gun, missed with one torpedo, hit with the next, and the Kashino went down.
The big ships carried other costs of the design. The blast of one triple turret was roughly twice that of a pair of 16-inch guns—strong enough, by Japanese calculation, to strip the clothing off a man on the open deck and knock him out. So the ship’s boats were stowed in hangars, and the first anti-aircraft guns were placed behind shields. During the Musashi’s calibration firing in July 1942, guinea pigs were put aboard to study what the blast did to living things.
The results of that test do not appear in Matsumoto’s later account. Yamato was the first Japanese warship with air conditioning, and sailors reportedly called her the most comfortable ship in the Navy. For all that comfort, her wartime service was limited. In the Sibuyan Sea on October 24, 1944, American carrier aircraft attacked the Musashi in wave after wave from mid-morning.
Her armored center held for hours while the unarmored forward end flooded compartment after compartment. By late afternoon she was down more than 26 feet by the head, her forecastle awash. At 7:36 that evening, she rolled over to port and sank. Of 2,399 men aboard, 1,023 were lost.
How many hits it took is not settled. Matsumoto’s 1953 account, drawn from her battle report, counts seven bombs and nine torpedoes by the end of the second attack, then ten more bombs and eleven more torpedo hits in the third. Researchers Bob Hackett and Sander Kingsepp, working from her detailed action report, give 19 torpedo hits and 17 bombs for the day, and note the count for the final attack is still disputed. Even the curtain at Nagasaki has the same problem: Matsumoto called it “shichirui,” more than 400 tons of rope, while contemporary files name palm fiber bought in about the same weight by the Sasebo Naval District.
Yamato herself went out on April 6, 1945, with a light cruiser and eight destroyers, bound for the American fleet off Okinawa. The next day, in the East China Sea southwest of Kyushu, carrier aircraft caught her. Her executive officer later counted at least seven large bombs and twelve aerial torpedoes, most on the port side. She rolled over and blew up, sending up smoke seen from 100 miles away.
Of 3,332 men aboard, 3,055 were lost. The papers went next. Most of the construction data for both ships burned in the confusion after the surrender in the summer of 1945, which is why the canal figures rest on thin ground. The 63,000 tons, the ten 16-inch guns, and the 23 knots come to us through Matsumoto, who set them down in a Japanese science magazine in 1950 while memory was still fresh.
He gives the results of the canal study, but his article names no surviving copy of it. The American Naval Technical Mission shipped two 18-inch guns home from Kure for study, each 75 feet long and weighing 180 tons. On November 18, 1944, one week out of Norfolk, the new battleship USS Missouri entered the Panama Canal westbound. Her beam was 108 feet 2 inches.
The lock chambers were 110 feet wide, which left less than a foot of water between her hull and each wall. Electric locomotives, which the canal calls mules, held her centered while the chambers filled and emptied. She came out at the Pacific end and steamed north for San Francisco, where she was fitted out as a fleet flagship.