Submersible Aircraft Carriers • Damn Interesting
On 09 September 1942, at about 6:00am Pacific War Time, a lookout on the US Oregon coast spotted a single incoming aircraft. The small, unmarked biplane plane sputtered and popped as it flew through the dawn mist. It slowly made its way over a heavily wooded area which was known to be particularly prone to forest fires, and dropped a pair of cylinders from a low altitude. Soon a column of smoke became visible from the forest as the strange plane turned around, its distinct engine noise fading back towards the ocean.
Immediately, Howard "Razz" Gardner-- the lookout who had first spotted the aircraft-- dove into the thick forest to battle the developing blaze. By the time the larger support crew penetrated the woods with their firefighting equipment four and a half hours later, Gardner and a fellow lookout had managed to wrestle the fire into submission. As the crew helped to mop up the last of the smoldering mess, the investigators found the remains of the offending ordnance. The fragments of the phosphorus incendiary bombs were stamped with Japanese markings.
The event came to be known as the Lookout Air Raid, and it marked the first time that the continental United States was bombed by an enemy aircraft. It was determined that the aircraft responsible was a Yokosuka E14Y floatplane, and that it had managed to reach the US coast because it had been launched from an unlikely platform: a Japanese submarine lingering just offshore.
The HMS M2 submarine launching its plane
The world's militaries had been dabbling in submersible aircraft carriers for decades, but the technology had long proven problematic. In the mid-1920s the British Royal Navy became the first to build a working prototype. An experimental single-plane hangar was fitted to the front of the conning tower on the HMS M2 submarine, providing the vessel with an airborne reconnaissance vehicle. The unarmed, lightweight biplane was crafted from wood, fabric, aluminum, and steel, and while not in use it sat nestled inside its tiny sealed cocoon with its delicate wings folded.
Once the submarine reached the surface, the plane's support crew could open the watertight vault door, extract the slumbering aircraft, unfurl its wings, and start the engine. Within minutes, a steam-powered catapult would heave the vehicle into the sky with its crew of two to scan the sea for enemy ships. When the scouting mission was complete the pilot would land the pontooned plane in the water alongside the submarine. A crane arm could then snag the aircraft and winch it back aboard, where it would once again be stuffed into its nook to await future flights.
The project showed some promise, but in 1932 the M2 mysteriously sunk with all hands lost. Though the exact circumstances were never determined, the sinking was blamed on water entering through the hangar door. Due to the design's dubious utility and inherent vulnerability, the Royal Navy decided to abandon the concept of submersible aircraft carriers.
Many other militaries continued to tinker with the contraptions, however, such as the French Surcouf submarine which was completed in 1934. It was the most massive submarine ever constructed, bristling with weapons and sporting a single-plane hangar in the style of the M2. When the French surrendered to the invading Nazis in 1940, the British Royal Navy blockaded the French ships in their ports to prevent them from falling into the hands of the German Kriegsmarine. Each was given the option to rejoin the war against Germany, or be destroyed.
The Surcouf
After a brief exchange of fire between the Surcouf and the British left several sailors dead, the French submarine relented.
The battle drove a wedge of suspicion between the submariners and their new commanders, but the giant sub worked in uneasy cooperation with the Allies in the early years of the war. Its true potential was never realized, however, due to a collision with an American freighter in 1942 which sunk the Surcouf with all hands lost. Due to the precarious nature of the French crew's allegiance, many suspected that the sinking was deliberate, though no evidence was ever found to support this theory.
Following the expensive failures of the M2 and the Surcouf, the United States and Italy abandoned their plans to construct similar vessels. But the Imperial Japanese Navy (IJN) managed to quietly master the art, and during the war the majority of their sub fleet included integrated aircraft hangars. Most of them-- including the I-25 which launched the attack in Oregon-- were single-plane hangars similar to the English and French efforts before them. But throughout the war the IJN significantly improved upon the submersible aircraft carrier concept.
Japan's first attempt to expand the platform was their AM Type submarines which carried a pair of bomber planes, but these suffered from poor underwater performance and they proved ineffective. The lessons learned from the AM Type, however, led to the development of the Sen Toku, Japan's most menacing oceangoing weapon. Translated literally as "secret submarine attack", the Sen Toku was developed for a single purpose: to launch a surprise attack against targets on the east coast of the United States. The Allies had won the war in Europe, so the bulk of the United States' military equipment was concentrated in the Pacific theater. Japanese military planners considered using their versatile new weapons to sneak up on Washington DC or New York, but they ultimately settled upon a plan to attack the the Panama Canal from the east where defenses were practically non-existent. The first two Sen Toku vessels set sail for Panama in mid-1945.
The I-400 Series and its Seiran bomber
The I-400 and I-401 were the largest submarines the world had ever seen, each of them crewed by almost 200 men. They had a range of 37,500 miles, enough to circumnavigate the globe one and a half times. Nestled inside each submarines' hangar was a set of three fast and agile dive bombers called Seiran, a Japanese word meaning "storm from a clear sky." Once the subs rounded the tip of Africa and crossed the Atlantic, their mission would be to emerge from the sea, open the giant hangar doors, and thrust their attack planes into the undefended skies of Panama. The Seiran would then bomb the locks unhindered. If successful, such an attack would spill Gatun Lake into the locks and ruin the machinery, severely crippling US shipping and supply efforts.
For months the submarine aircraft carrier crews practiced and perfected their attack strategy for the Panama run. None of the pilots were expected to survive the attack, so each was presented with a tokko short sword which symbolized the ultimate sacrifice. It was to be an utterly victorious surprise attack reminiscent of Pearl Harbor.
Shortly after getting underway, however, the Sen Toku and their attendant submarines were ordered to return in order to deflect an imminent Allied invasion of the Japanese homeland. The fleet turned back and steamed for the Allied base at Ulithi Atoll , but as they approached their target the crews received orders to catapult their planes into the sea and fire their torpedoes without arming them. Japan had surrendered in the wake of a pair of atomic attacks. The war was over. Captain Ariizumi, the commander of the submarine fleet, chose suicide over the shame of surrendering to the Americans.
In late August 1945, about two weeks after the end of hostilities, a United States Navy destroyer intercepted the unfamiliar Japanese submarines as they made for their home port. As the US sailors sidled alongside, they were astonished by the size of the behemoths. They were much more massive than any built before them, four hundred feet in length and three times larger than typical submarines.
The crew of the I-400 shortly after surrender
In addition to their empty airtight hangars, each Sen Toku had four anti-aircraft guns, eight torpedo tubes, and a sizable deck cannon. The subs were each powered by four 7,700 horsepower diesel engines, and they could operate at a depth of 330 feet. Clearly the I-400 series submarines would have been formidable weapons had they even seen action.
Once the virgin vessels reached Japan's Sasebo Bay, a team of US Navy experts immediately began to scrutinize the technology of the three working Sen Toku vessels. The technicians marveled at the huge hangars and the innovative figure-eight hull reinforcements, but their investigations were cut short when they were informed that the Soviets were sending a team to inspect the captured submarines. Rather than allowing the Soviets access to the advanced technology, the Americans instituted Operation Road's End. Two of the subs were packed with C-2 explosives and scuttled off the Japanese coast, and the others were sailed to Hawaii where further secret inspections occurred before they were also destroyed at sea.
The Japanese Sen Toku were the last of their kind. No submersible aircraft carriers have been built since, though the idea does occasionally spark the interest of modern militaries as a means to approach with stealth and attack without warning. In spite of the technical challenges involved, the concept is certainly strategically appealing. Indeed, had the I-400 vessels set off for the Panama Canal just a few months sooner, the storm they brought with them might have altered the course of the war by shattering the critical US supply route through Panama. In some ways, the Allies' victory in the Second World War was much narrower than history implies.
Written by Alan Bellows, posted on 09 April 2007. Alan is the founder/designer/head writer/managing editor of Damn Interesting.
On 09 September 1942, at about 6:00am Pacific War Time, a lookout on the US Oregon coast spotted a single incoming aircraft. The small, unmarked biplane plane sputtered and popped as it flew through the dawn mist. It slowly made its way over a heavily wooded area which was known to be particularly prone to forest fires, and dropped a pair of cylinders from a low altitude. Soon a column of smoke became visible from the forest as the strange plane turned around, its distinct engine noise fading back towards the ocean.
Immediately, Howard "Razz" Gardner-- the lookout who had first spotted the aircraft-- dove into the thick forest to battle the developing blaze. By the time the larger support crew penetrated the woods with their firefighting equipment four and a half hours later, Gardner and a fellow lookout had managed to wrestle the fire into submission. As the crew helped to mop up the last of the smoldering mess, the investigators found the remains of the offending ordnance. The fragments of the phosphorus incendiary bombs were stamped with Japanese markings.
The event came to be known as the Lookout Air Raid, and it marked the first time that the continental United States was bombed by an enemy aircraft. It was determined that the aircraft responsible was a Yokosuka E14Y floatplane, and that it had managed to reach the US coast because it had been launched from an unlikely platform: a Japanese submarine lingering just offshore.
The HMS M2 submarine launching its plane
The world's militaries had been dabbling in submersible aircraft carriers for decades, but the technology had long proven problematic. In the mid-1920s the British Royal Navy became the first to build a working prototype. An experimental single-plane hangar was fitted to the front of the conning tower on the HMS M2 submarine, providing the vessel with an airborne reconnaissance vehicle. The unarmed, lightweight biplane was crafted from wood, fabric, aluminum, and steel, and while not in use it sat nestled inside its tiny sealed cocoon with its delicate wings folded.
Once the submarine reached the surface, the plane's support crew could open the watertight vault door, extract the slumbering aircraft, unfurl its wings, and start the engine. Within minutes, a steam-powered catapult would heave the vehicle into the sky with its crew of two to scan the sea for enemy ships. When the scouting mission was complete the pilot would land the pontooned plane in the water alongside the submarine. A crane arm could then snag the aircraft and winch it back aboard, where it would once again be stuffed into its nook to await future flights.
The project showed some promise, but in 1932 the M2 mysteriously sunk with all hands lost. Though the exact circumstances were never determined, the sinking was blamed on water entering through the hangar door. Due to the design's dubious utility and inherent vulnerability, the Royal Navy decided to abandon the concept of submersible aircraft carriers.
Many other militaries continued to tinker with the contraptions, however, such as the French Surcouf submarine which was completed in 1934. It was the most massive submarine ever constructed, bristling with weapons and sporting a single-plane hangar in the style of the M2. When the French surrendered to the invading Nazis in 1940, the British Royal Navy blockaded the French ships in their ports to prevent them from falling into the hands of the German Kriegsmarine. Each was given the option to rejoin the war against Germany, or be destroyed.
The Surcouf
After a brief exchange of fire between the Surcouf and the British left several sailors dead, the French submarine relented.
The battle drove a wedge of suspicion between the submariners and their new commanders, but the giant sub worked in uneasy cooperation with the Allies in the early years of the war. Its true potential was never realized, however, due to a collision with an American freighter in 1942 which sunk the Surcouf with all hands lost. Due to the precarious nature of the French crew's allegiance, many suspected that the sinking was deliberate, though no evidence was ever found to support this theory.
Following the expensive failures of the M2 and the Surcouf, the United States and Italy abandoned their plans to construct similar vessels. But the Imperial Japanese Navy (IJN) managed to quietly master the art, and during the war the majority of their sub fleet included integrated aircraft hangars. Most of them-- including the I-25 which launched the attack in Oregon-- were single-plane hangars similar to the English and French efforts before them. But throughout the war the IJN significantly improved upon the submersible aircraft carrier concept.
Japan's first attempt to expand the platform was their AM Type submarines which carried a pair of bomber planes, but these suffered from poor underwater performance and they proved ineffective. The lessons learned from the AM Type, however, led to the development of the Sen Toku, Japan's most menacing oceangoing weapon. Translated literally as "secret submarine attack", the Sen Toku was developed for a single purpose: to launch a surprise attack against targets on the east coast of the United States. The Allies had won the war in Europe, so the bulk of the United States' military equipment was concentrated in the Pacific theater. Japanese military planners considered using their versatile new weapons to sneak up on Washington DC or New York, but they ultimately settled upon a plan to attack the the Panama Canal from the east where defenses were practically non-existent. The first two Sen Toku vessels set sail for Panama in mid-1945.
The I-400 Series and its Seiran bomber
The I-400 and I-401 were the largest submarines the world had ever seen, each of them crewed by almost 200 men. They had a range of 37,500 miles, enough to circumnavigate the globe one and a half times. Nestled inside each submarines' hangar was a set of three fast and agile dive bombers called Seiran, a Japanese word meaning "storm from a clear sky." Once the subs rounded the tip of Africa and crossed the Atlantic, their mission would be to emerge from the sea, open the giant hangar doors, and thrust their attack planes into the undefended skies of Panama. The Seiran would then bomb the locks unhindered. If successful, such an attack would spill Gatun Lake into the locks and ruin the machinery, severely crippling US shipping and supply efforts.
For months the submarine aircraft carrier crews practiced and perfected their attack strategy for the Panama run. None of the pilots were expected to survive the attack, so each was presented with a tokko short sword which symbolized the ultimate sacrifice. It was to be an utterly victorious surprise attack reminiscent of Pearl Harbor.
Shortly after getting underway, however, the Sen Toku and their attendant submarines were ordered to return in order to deflect an imminent Allied invasion of the Japanese homeland. The fleet turned back and steamed for the Allied base at Ulithi Atoll , but as they approached their target the crews received orders to catapult their planes into the sea and fire their torpedoes without arming them. Japan had surrendered in the wake of a pair of atomic attacks. The war was over. Captain Ariizumi, the commander of the submarine fleet, chose suicide over the shame of surrendering to the Americans.
In late August 1945, about two weeks after the end of hostilities, a United States Navy destroyer intercepted the unfamiliar Japanese submarines as they made for their home port. As the US sailors sidled alongside, they were astonished by the size of the behemoths. They were much more massive than any built before them, four hundred feet in length and three times larger than typical submarines.
The crew of the I-400 shortly after surrender
In addition to their empty airtight hangars, each Sen Toku had four anti-aircraft guns, eight torpedo tubes, and a sizable deck cannon. The subs were each powered by four 7,700 horsepower diesel engines, and they could operate at a depth of 330 feet. Clearly the I-400 series submarines would have been formidable weapons had they even seen action.
Once the virgin vessels reached Japan's Sasebo Bay, a team of US Navy experts immediately began to scrutinize the technology of the three working Sen Toku vessels. The technicians marveled at the huge hangars and the innovative figure-eight hull reinforcements, but their investigations were cut short when they were informed that the Soviets were sending a team to inspect the captured submarines. Rather than allowing the Soviets access to the advanced technology, the Americans instituted Operation Road's End. Two of the subs were packed with C-2 explosives and scuttled off the Japanese coast, and the others were sailed to Hawaii where further secret inspections occurred before they were also destroyed at sea.
The Japanese Sen Toku were the last of their kind. No submersible aircraft carriers have been built since, though the idea does occasionally spark the interest of modern militaries as a means to approach with stealth and attack without warning. In spite of the technical challenges involved, the concept is certainly strategically appealing. Indeed, had the I-400 vessels set off for the Panama Canal just a few months sooner, the storm they brought with them might have altered the course of the war by shattering the critical US supply route through Panama. In some ways, the Allies' victory in the Second World War was much narrower than history implies.
Written by Alan Bellows, posted on 09 April 2007. Alan is the founder/designer/head writer/managing editor of Damn Interesting.
