Chinese and the US forces were locked in a reconnaissance and electronic warfare tussle in the lead-up to and after US House Speaker Nancy Pelosi's trip to Taiwan, according to military sources and defence analysts.
But not all of it was successful, according to sources close to the Chinese military.
State broadcaster CCTV reported the Chinese military used naval and air forces in multiple locations to conduct "full tracking and surveillance" against the US Air Force transport aircraft flying Pelosi and her delegation from Kuala Lumpur to Taipei on August 2.
The tracking was aimed at "deterrence", the report quoted PLA Major General Meng Xiangqing, from the PLA National Defence University, as saying.
However a source said the People's Liberation Army's tracking efforts - which involved jets and Type 055 destroyers - failed.
"The PLA deployed some electronic warfare aircraft such as the J-16D and warships to try to locate Pelosi's aircraft, but were not successful," the source said.
"Almost all the PLA electronic warfare equipment couldn't work properly because they were all jammed by electronic interference by the American aircraft strike group sent by the Pentagon to escort her."
On the flight, Pelosi's aircraft took an unusually circuitous route by heading southeast towards the Indonesian part of Borneo, then turning north to fly along the eastern part of the Philippines.
He Yuan Ming, an independent airpower analyst, said it was not surprising that the Chinese vessels did not detect the flight.
"Even if the Type 055 (destroyer's) radar is said to be 500km (310 miles), its effective range in the real world would be much less," He said.
"Couple this with the vast operating area as well as the Type 055's relative newness both in terms of its hardware (capabilities) and software (crew), there should be little surprise that the PLA (naval) cruiser could not locate (Pelosi's plane)."
Pelosi's trip was followed by a series of unprecedented PLA war games encircling Taiwan.
On the second day of the exercises, the US sent at least seven reconnaissance and early warning aircraft to waters near Taiwan, according to the Beijing-based South China Sea Strategic Situation Probing Initiative.
The deployment included a RC-135V and RC-135S for missile surveillance, three P-8A maritime anti-submarine planes, three E-3G spy jets and one U-2S high-altitude monitor plane, supported by six KC-135 refueling aircraft.
Andrei Chang, editor-in-chief of Canada-based Kanwa Asian Defence, said that with its technology it was very likely that the American navy realised that the PLA had deployed submarines to waters off Taiwan, despite silence on both sides over the involvement of the vessels in the war games.
Chang also said it was likely the US played a role behind the scenes in Japan and Taiwan.
During the drills, Taiwanese authorities said the PLA sent 11 ballistic missiles into waters to the north, south and east of the island.
Japan said five of those missiles fell within its exclusive economic zone, an area that China does not recognise.
"Beijing declined to reveal how many ballistic missiles it had launched, while Taipei and Tokyo's announcement could be seen as a warning to the mainland that they are able to detect and track the PLA missiles, which is part of the electronic warfare tactics," Chang said.
He said the missiles would have been tracked by the Leshan radar station in Hsinchu county on Taiwan.
Operating since 2013, the system can detect a missile launched from as far away as 5,000km and track projectiles in motion in great detail, even from a distance of 2,000km - a range that covers mainland China and the entire South China Sea.
"The long-range early warning radar system on Leshan was established under the assistance of the US, with some American experts still stationed in the radar centre," Chang said.
The first source said electronic warfare between the PLA and US military went back to the 1995-96 Taiwan Strait crisis when American forces jammed almost all the PLA's military radar systems during its missile tests.
"That's the key reason that prompted China to develop its own BeiDou Satellite Navigation System," the source said, adding that both sides were keen to size up the other's strength in the area.
"Both China and the US wanted to examine each other's electronic warfare capabilities this time. The PLA is especially keen to make sure its technology is strong enough to cope with a possible Taiwan contingency."
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