(CNN) — In early July 1944, on a tiny island in the Pacific Ocean, the United States clinched a devastating defeat over Japan in one of the bloodiest battles of World War II.
Some 29,000 Japanese troops, almost the entire force Tokyo put on Saipan, in the Northern Marianas, were killed. U.S. losses totaled almost 3,000 dead and more than 10,000 wounded.
It was a pivotal moment in the war.
Soon after the Battle of Saipan, the U.S. took the nearby islands of Tinian and Guam. On all three islands, the US built runways to accommodate heavy B-29 bombers, the biggest bombers in World War II.
Within months, those B-29s had burned vast swathes of Tokyo and pounded factories supporting the Japanese war machine.
At one point, the US airfield on Tinian — just 5 miles (9 kilometers) from Saipan — was the largest airport in the world, with six runways accommodating almost 270 B-29s.
As the U.S. thrived on these islands, Japan crumbled.
In August 1945, B-29s flying from Tinian dropped atomic bombs on Hiroshima and Nagasaki, spurring Japan's surrender.
When considering current tensions in the South China Sea, where China has built airstrips, the Battle of Saipan offers important lessons that should not be ignored.
The South China Sea
Controversy has been building for years over the South China Sea — essentially, 1.3 million square miles of international or contested waters and islands.
China has been building runways and military facilities on reclaimed shoals and sandbars there to reinforce its territorial claims in the sea, something the U.S. says endangers free passage.
These facilities also give China a greater strike range by allowing it to deploy aircraft from previously unoccupied territory.
"Chinese long-range bombers if staging through the islands is certainly an issue," says Peter Layton, a military analyst at Australia's Griffith Asia Institute. "That would allow air-launched cruise missile strikes into northern Australia airfields and ports, (placing) any USAF bombers and tankers deployed there at risk."
That means places such as RAAF Base Tindal, near Darwin in northern Australia, must now be defended against a "sophisticated threat," says Layton.
"This is a major change," he adds, noting that such bases used to be thought of as "sanctuaries well outside Chinese strike range."
Underscoring the seriousness of the matter, a 2018 report from the RAND Corp. think tank recommended joint U.S.-Australia air defense exercises as a deterrent against any possible action from China.
U.S. and Australian forces regularly train together in Darwin, and as recently as May U.S. and Royal Australian Airforce (RAAF) pilots took part in a bilateral training exercise off Australia's Northern Territory.
An extra 1,000 miles of range
Carl Schuster, a former U.S. Navy captain and instructor at Hawaii Pacific University, says that having runways in the South China Sea effectively adds more than 1,000 miles to the range of China's biggest bombers, the H-6K.
Those aircraft can be armed with long-range cruise missiles, which allow the bombers to stay out of the reach of anti-aircraft defenses.
Schuster makes another point — one that didn't necessarily apply in the case of Saipan, but certainly looms large 75 years later. While in 1944, the U.S. had one specific enemy in this region — Japan — in 2019, China seeks to exert influence over a range of countries.
"By controlling the South China Sea, China can project its air and sea power to the Pacific Ocean's western entry points, Malacca, Sundra and Lombok Straits," Schuster says.
The means China can "ensure entry and exit of its maritime forces and commerce to and from the Indian Ocean, through which 45% of China's exports and 60% of raw material imports must pass," he adds.
The influence of those runways and military facilities also pushes northwards.
"That control also extends China's defensive buffer to the southeast by nearly 600 miles, (and) all but ensures leverage against Japan and Taiwan, since those waters are critical to those countries' economies," Schuster says.
China says the runways and military assets it has installed in the South China Sea are for defense purposes only, to protect what it claims is its sovereign territory.
"The Chinese People's Liberation Army needs to deploy fighter jets at military airports to protect the territorial airspace and sea," state-sanctioned Global Times quoted Chinese air defense expert Fu Qianshao as saying.
Schuster said the deployment of those fighter jets sent a much broader message.
"It ... makes a statement that they can extend their air power reach over the South China Sea as required or desired," he said.
While small islands can help a country project power with aircraft and missiles, they also offer a more mundane but vital advantage for any military — something Saipan gave the Americans in World War II: a place to shorten the supply chain and stage ground forces.
Saipan, for example, became a vital way to support US operations on islands closer to the Japanese mainland, such as Okinawa, making those campaigns easier to sustain. In the South China Sea, island facilities could give PLA ships safe harbors where they can rest and replenish without going back to bases on the Chinese mainland.
While no one is contending that any conflict — let alone one on the scale of World War II — is an imminent risk in the South China Sea, China's islands would give it a distinct advantage in the event of war.
And, as Japan failed to recover from the losses sustained on Saipan in 1944, some wonder if it's too late for the US and its allies and partners in Asia to reverse the gains China has made by constructing the islands.
They "allow China to dominate the central ASEAN region," Layton said.
"No regional nation ... can realistically counter the threat the islands now pose."
This story was first published on CNN.com. "Losing one island cost Japan a war. That's a warning for the South China Sea."