IJN Kaga

Kaga began life as something else entirely. She was laid down in 1920 as a battleship of the Tosa class, one of the giants of Japan’s planned battle fleet — until the Washington Naval Treaty of 1922 halted the great battleship race and condemned her half-built hull to the scrapyard.

She was saved by an accident. When the great earthquake of 1923 wrecked the battlecruiser Amagi, already earmarked for conversion into an aircraft carrier, the navy substituted Kaga’s spare battleship hull in her place. Rebuilt with a flight deck, she was commissioned as a carrier on 31 March 1928 — a battleship reborn as a ship of the air age.

As first completed she was an awkward experiment, with stepped flying-off decks and long horizontal funnels venting down her sides. Between 1934 and 1935 she was rebuilt almost from the waterline up: a single full-length flight deck, a small starboard island, and a distinctive trunked funnel curving down to starboard. The reconstruction raised her to some 38,200 tonnes and let her operate the largest air group of any Japanese carrier — around ninety aircraft.

That size came at a price. Her machinery, even rebuilt to about 127,000 shp, could push her to only some 28 knots — several knots slower than the fast fleet carriers Hiryū and Sōryū she served alongside, and a persistent tactical handicap. But she carried more aircraft than any of them, and in the doctrine of massed carrier air power that Japan was pioneering, that counted for a great deal.

Her battleship ancestry left a visible mark. Kaga carried ten 200 mm guns — eight-inch weapons of the sort that armed heavy cruisers — mounted in casemates along her hull, because in the 1920s nobody was certain what a carrier was for. The prevailing assumption was that she might have to fight surface ships herself, and a flight deck was not yet trusted to be a weapon in its own right.

By 1941 that assumption looked absurd, and the guns were dead weight: a carrier that came within 200 mm gun range of an enemy warship had already lost. What she needed instead was anti-aircraft armament, and there the Japanese carriers were consistently weak — too few heavy guns, light automatic weapons of limited reach, and fire control that could not handle several attacks at once. The ship was armed against the war of her design and under-armed against the war she got.

Kaga went to war long before Pearl Harbor. Her aircraft were in action over Shanghai in 1932, flying some of the earliest carrier air strikes in history, and again from 1937 in the Second Sino-Japanese War, bombing Chinese cities and airfields far inland.

These operations were a proving ground for the men and the methods that would later stun the world. The aircrews who honed their skills over China became the veteran core of the Kidō Butai, and the techniques of massed, long-range carrier strikes were rehearsed in those campaigns years before they were unleashed on the United States Navy.

On 7 December 1941 Kaga was one of the six carriers that struck Pearl Harbor. Her dive- and torpedo-bombers were among the most destructive of the morning — and she paid for it, losing more aircraft than any other carrier in the strike. Through the months that followed she ranged with the Kidō Butai across the Pacific, from the devastating raid on Darwin to the conquest of the Dutch East Indies.

She missed the fleet’s triumphant Indian Ocean raid of April 1942, having run aground on a reef and returned to Japan for repairs. It was a lucky escape that only postponed her end: when the Kidō Butai sailed for Midway two months later, Kaga sailed with it.

On the morning of 4 June 1942 the SBD Dauntless dive bombers of the Enterprise found the Japanese carriers with no fighters at altitude to stop them: the covering Zeros had been drawn down to sea level destroying the American torpedo squadrons. About four bombs struck Kaga in the space of a few moments. One burst near the bridge and killed the captain and most of the command staff; the others went into hangars packed with fuelled and armed aircraft, and the ship became an inferno almost at once.

The famous version of this story — that the Japanese were five minutes from launching a strike that would have changed everything — does not survive the records. Modern research on Japanese sources, above all Parshall and Tully’s Shattered Sword, established that no strike was spotted on deck and that launching one was still 30 to 45 minutes away. What destroyed the carriers was not a near miss of timing but the state of their hangars: aircraft below decks, fuel lines charged, ordnance being changed. Kaga burned all day, was abandoned that evening and sank with more than 800 of her crew — the heaviest loss of any of the four carriers lost that day. Her wreck was found on the deep Pacific floor in 2019.

Kaga was the odd giant of the Kidō Butai: a converted battleship hull, the slowest of the fast carriers at some 28 knots, still carrying cruiser guns she could never usefully fire — and yet the ship with the largest air group of the six, and among the heaviest hitters at Pearl Harbor and after. She is the clearest illustration that in carrier warfare the hull matters far less than what flies off it.

She died in the space of a single morning, one of four irreplaceable carriers lost in minutes that turned the Pacific war. The loss that mattered most was not the tonnage but the aircrews — the veterans trained over China and blooded from Pearl Harbor to Ceylon, a cadre Japan had no system for replacing at the rate it was now losing them. The age of the carrier that Kaga had helped pioneer passed, that morning, decisively into American hands.

• Jonathan Parshall & Anthony Tully, Shattered Sword: The Untold Story of the Battle of Midway (Potomac, 2005).
• Mark R. Peattie, Sunburst: The Rise of Japanese Naval Air Power (Naval Institute Press).
• Gordon W. Prange, Miracle at Midway (McGraw-Hill, 1982).