Here's What You Need to Know: An hour before the air attack, a squadron of tiny Japanese midget submarines attempted to slip into Pearl Harbor's defenses.

On Dec. 7, 1941, the aircraft of the Imperial Japanese Navy rained devastation upon the U.S. naval base at Pearl Harbor, Hawaii. But Japanese warplanes didn’t actually fire the first shots that brought America into a massive Pacific War.

An hour before the air attack, a squadron of tiny Japanese midget submarines attempted to slip into the harbor’s defenses, like burglars in the night, to wreak havoc on Battleship Row. Unlike the aerial assault, the sailors failed spectacularly — and the story is often forgotten.

By the 1930s, Imperial Japan and the United States were set on a collision course. Tokyo’s decision to invade China in 1931 and intensify their brutal campaign six years had provoked ultimately irrevocable tensions.

The United States responded to the incursion into China with increasing sanctions, culminating with an embargo on petroleum in July 1941 that crippled the Japan’s economy. Japanese military leaders had wanted to capture the Dutch East Indies to secure its oil wealth, but knew it would trigger war with the Unites States.

While U.S.-Japanese negotiations came within striking distance of a peace agreement, Roosevelt was a hard bargainer, demanding Japan’s leaders order a complete withdrawal from China. They refused.

Thus, Japanese Adm. Yamamoto began planning for a “short victorious war.” The key to this idea was knocking out the battleships of the U.S. Pacific fleet at their home base of Pearl Harbor, Hawaii to buy the Japanese Army time to complete the conquest of the Western Pacific.

Along with a massive air strike from a Japanese carrier task force would constitute the main attack, the Navy coordinated the undersea assault using midget submarines.

During World War II, Japan, England, Italy and Germany all employed midget submarines to stealthily infiltrate shallow, defended harbors and attack vulnerable capital ships. The Japanese Navy’s midget submarines had hidden their developments by calling the ships Type A Kō-hyōteki , or “Target A”

Japanese officials hoped the designation would deceive foreign analysts into believing the 78-feet long submarines were actually mock ships for naval gunnery practice. In reality, each of the 46-ton subs had a crew of two and was armed with two 450-millimeter Type 97 torpedoes with 800 pound warheads.

The little submarines could sprint up to 26 miles per hour submerged, but could not dive deeper than 100 meters. More importantly, the Type As had no engine and ran purely on batteries.

This gave the diminutive vessels a maximum endurance of 12 hours at speeds of 6 miles per hour. The subs often ran out of power much faster in real combat.

As a result, a larger submarine mothership had to bring the Type As close to the target area. Even so, the battery limitations made it unlikely the midget sub could make it back to safety. Each one had a 300-pound scuttling charge as a self-destruct device.

Just getting to the designation was difficult enough. Since the small boats were difficult to control even while swimming in a straight line, crews had to manually move lead weights backwards and forwards to stabilize the vessel.

With these obvious issues, on Oct. 19, 1941, the Japanese Navy began modifying five Type A subs with improved pneumatic steering devices, as well as net-cutters and guards for fending off anti-submarine nets. Workers at the Kure Naval District painted over the submarine’s running lights to help hide them from enemy spotters.

Afterwards the midgets went to the Kamegakubi Naval Proving Ground and crews loaded them onto the backs of five large Type C-1 submarines, the I-16, I-18, I-20, I-22 and I-24. On Nov. 25, 1941, The motherships set sail for Pearl Harbor.

While on route, the so-called “Special Attack Unit” received the coded message “Climb Mount Niitaka 1208.” This meant authorities in Tokyo had not found a diplomatic solution and signaled the go-ahead for the Pearl Harbor attack.

On Dec. 6, 1941, the C-1s swam to points within 12 miles of Pearl Harbor. Then, between the hours of midnight and 3:30 A.M. the next day, the ships released their deadly payloads.

For the crews, getting inside Pearl Harbor posed a serious challenge. Ships could only enter the port through a 65 foot-deep channel guarded by an anti-submarine net 35 feet deep.

Boats on either side of the nets tugged them apart to allow friendly boats to pass through. On top of that, American destroyers prowled in a five mile arc around the harbor entrance, assisted by watchful eyes on orbiting PBY Catalina maritime patrol planes.

On paper, the Japanese intended for the submarine attack to work as well-planned heist. The midget subs would sneak in by following American ships passing through openings in the anti-submarine net.

Then the subs would lay low until the air attack sowed chaos throughout the harbor, at which point they would unleash their torpedoes at any American battleships that survived the bombing. Afterwards, the midget subs would slip away to Hawaii’s Lanai Island.

The submarines I-68 and I-69 would wait no more than 24 hours to pick up any surviving crew. The Japanese did not plan to recover the Type As themselves.

If everything worked out right, American officials would only receive the Japanese declaration of hostilities mere moments before the attack commenced. However, things didn’t go according to plan.

Just before 4:00 A.M., the minesweeper USS Condor spotted the periscope of the midget submarine Ha-20 and called over the destroyer USS Ward to search the area.

Just over an hour and a half later, crew aboard the Ward spotted a periscope in the wake of the cargo ship Antares as it passed through the anti-submarines nets. While a PBY Catalina patrol plane dropped smoke markers near the sub’s position, the Ward charged the sub.

Gunners fired two shots from the ship’s 4-inch main gun at less than 100 meters and followed up with four depth charges. The Type A vanished into the water.

For the crews, getting inside Pearl Harbor posed a serious challenge. Ships could only enter the port through a 65 foot-deep channel guarded by an anti-submarine net 35 feet deep.

Boats on either side of the nets tugged them apart to allow friendly boats to pass through. On top of that, American destroyers prowled in a five mile arc around the harbor entrance, assisted by watchful eyes on orbiting PBY Catalina maritime patrol planes.

On paper, the Japanese intended for the submarine attack to work as well-planned heist. The midget subs would sneak in by following American ships passing through openings in the anti-submarine net.

Then the subs would lay low until the air attack sowed chaos throughout the harbor, at which point they would unleash their torpedoes at any American battleships that survived the bombing. Afterwards, the midget subs would slip away to Hawaii’s Lanai Island.

The submarines I-68 and I-69 would wait no more than 24 hours to pick up any surviving crew. The Japanese did not plan to recover the Type As themselves.

If everything worked out right, American officials would only receive the Japanese declaration of hostilities mere moments before the attack commenced. However, things didn’t go according to plan.

Just before 4:00 A.M., the minesweeper USS Condor spotted the periscope of the midget submarine Ha-20 and called over the destroyer USS Ward to search the area.

Just over an hour and a half later, the crew aboard the Ward spotted a periscope in the wake of the cargo ship Antares as it passed through the anti-submarines nets. While a PBY Catalina patrol plane dropped smoke markers near the sub’s position, the Ward charged the sub.

Gunners fired two shots from the ship’s 4-inch main gun at less than 100 meters and followed up with four depth charges. The Type A vanished into the water.

Taking on seawater caused the batteries to spew out deadly chlorine gas. A depth charge attack finally knocked out the periscope and disabled the midget submarine’s remaining undamaged torpedo.

Sakamaki decided to try and sail their stricken craft back to the mothership. He and Inagaki passed out as the choking gasses filling the inside of their ship.

The two managed to regain consciousness in the evening and decided to ground their sub near the town of Waimānalo to the east. However, they crashed on yet another reef.

A patrolling PBY bomber dropped depth charges on the crippled submarine. Sakamaki decided to abandon ship and attempted to detonate the scuttling charge — but even the ship’s self-destruct device failed to work.

Sakamaki succeeded in swimming ashore and promptly fell unconscious. His crewmate drowned.

The following morning, Hawaiian soldier David Akui captured a Japanese sailor. The first Japanese prisoner of war of World War II, Sakamaki refused to cooperate during his interrogation, requesting that he be executed or allowed to commit suicide.

The Japanese military became aware of his capture but officially claimed that all of the submarine crews had been lost in action. A memorial to the Special Attack Unit omitted his name.