How much of a threat are Chinese spy balloons?

A surveillance balloon drifting on the high-altitude breeze is not cutting-edge spyware. But the Chinese device discovered over the north-western US state of Montana has proven to be more effective as a diplomatic irritant between the world’s largest economies.

Secretary of state Antony Blinken cancelled a trip to China this weekend in response to the incursion, even as Beijing claimed it was a “civilian airship used for research” that had been blown off course.

The Pentagon said on Thursday it was tracking the balloon over Montana, where the US has nuclear intercontinental ballistic missile silos. It added that President Joe Biden had decided against shooting it down because of the risk to civilians.

The Pentagon said the decision also reflected the fact that the balloon provided China with little information that it could not obtain from satellites. Canada said it was tracking the balloon in conjunction with the US, but was also monitoring a “second potential incident”.

What is a spy balloon?

First deployed during the French revolutionary wars, balloons operated by spies with binoculars were used during the American civil war to detect enemy troop movements.

They were used extensively during the cold war, as the US and Soviet Union sought ways to monitor each other’s military.

Lacking propulsion, they are subject to the vagaries of wind currents. But modern versions of the low-cost devices can house cameras, radars and radio devices.

Why would one be used?

While the vast improvement in satellite technology and proliferation of spy satellites in recent decades, plus the increased use of unmanned drones, has rendered surveillance balloons technologically largely obsolete, they are still being used, particularly for non-military observation.

The Pentagon said the balloon did not provide China with capabilities that went beyond its spy satellites, but military and intelligence analysts said that the slow speed and high altitude of balloons — they usually operate at around 80,000ft, far higher than commercial airliners — does allow them to record over a larger area than satellites in orbit and pick up more detail.

They are also harder to spot than metal drones or aircraft using traditional anti-surveillance equipment such as radar, while they can remain in the air for weeks, providing a lengthy assessment of activity on the ground.

In 2019 the Pentagon was revealed to be having its own spy balloon renaissance, launching a pilot scheme to “provide a persistent surveillance system to locate and deter narcotic trafficking and homeland security threats”.

What might China have been hoping to achieve?

The Pentagon said the balloon was detected in US airspace earlier this week after crossing Canada. Montana and other states in the region, including North Dakota, house some of the bases from which the US would launch nuclear weapons in the event of war. “Clearly, the intent of this balloon is for surveillance,” a US official said.

Malmstrom Air Force Base, home to the US air force’s 341st Missile Wing and silos for 150 intercontinental ballistic missiles, is based in Montana, which is otherwise known for mountains and prairies.

US officials said the Pentagon had taken steps to prevent the balloon from recording important information.

It is not unprecedented for the US and China to accuse each other of spying. Beijing has long claimed that American ships and planes close to its borders are conducting surveillance. The US insists that its surveillance operations are carried out in international waters and airspace. Last year, Admiral John Aquilino, the head of US Indo-Pacific command, flew in a spy plane over the South China Sea.

Meanwhile, other spy balloons have been observed over US territory in the past — though not typically lingering as long as the one spotted this week.

Some analysts suggested that the balloon was either directed towards the US by mistake, or that the intention was for it to be discovered, as a means of reminding Washington to be on its guard.

Blake Herzinger, a non-resident fellow at the American Enterprise Institute, said on Twitter before China gave its explanation that “we need to at least consider the possibility that this was a mistake”.

“Beijing isn’t insane. Sending a balloon over the continental United States to collect against something they can surely do clandestinely from space is a totally unnecessary risk,” he added.

What is the likely diplomatic impact?

The cancellation of Blinken’s two-day trip is already a major consequence of the incident. Washington’s chief envoy had been expected to meet Chinese president Xi Jinping, on a trip that would have made him the first Biden administration cabinet secretary to visit China and the first secretary of state to travel to the country in more than five years.

Relations between the superpowers are already on edge. Blinken’s trip was part of efforts to stabilise tensions after talks between Biden and Xi in November. The leaders agreed at that meeting that they should attempt to set a floor under the relationship, which has sunk to its lowest level since the countries established diplomatic relations in 1979.

Some Republicans in Congress, including Tom Cotton, a senator from Arkansas, had earlier seized on the news of the balloon to call on Blinken to cancel his visit. They have also criticised the White House for allowing such an incursion.

But Michael McCaul, the Republican head of the House foreign affairs committee, said Blinken should have gone, to tell “Chairman Xi and his government that their military adventurism will no longer be tolerated”.

“I don’t think the [Chinese] leadership understands how big a political deal this spy balloon is becoming in DC,” said Bill Bishop, a US-China analyst. “Just darkens even more an already rapidly darkening mood on [Capitol] Hill.”

What happens now?

A Chinese statement released on Friday said: “The Chinese side regrets the unintended entry of the airship into US airspace due to force majeure. The Chinese side will continue communicating with the US side and properly handle this unexpected situation.”

The US said earlier that it had conveyed its displeasure to China through various channels, but it was unclear how Washington might seek to escalate or defuse the issue with Beijing. Canada on Thursday summoned the Chinese ambassador to Ottawa to register its objections.

While the diplomatic weather remains squally, Biden’s decision not to shoot down the balloon means that it is likely to continue as it has done so far — drifting whichever way the wind takes it.