China proved with its reckless 2007 anti-satellite test that it does not play by Western rules. China will risk Kessler Syndrome to achieve its goals. Its actions in the South China Sea demonstrate that it considers that body of water to be its private lake, just as Russia considers the Kerch Strait to be its private lake. But the jury's out on the rest of China's intentions. Taking out GPS and/or spy satellites is no doubt on their wish list.
As I wrote before, the US Navy has bet the farm on carrier-based aircraft with a range of around 600 miles. But China saw the flaw in that thinking and developed hypersonic missiles that travel twice that distance, effectively keeping US carriers at bay. Current thinking is to employ tanker aircraft, but someone at the Navy Department is asleep at the wheel. Chinese aircraft could fire multiple, long-range missiles at the tankers. The task would be made easier by F-35s providing fighter protection, as their stealth characteristics would allow Chinese missiles to see the tanker as the only target in the sky.
Neither Serbia nor Russia have officially revealed how Serbian Colonel Zoltán Dani's 250th Missile Brigade shot down an F-117 in March 1999. Stealth aircraft do not have a cloak of invisibility; their design merely diminishes radar signatures. Dani used a different frequency for his crew's radar, a technique which could be used by Russia or China.
Just as the US Navy has wisely returned to teaching the sextant, it must consider other factors. Both China and Russia are diligently working on jamming GPS, as they know that the entire US military is dependent upon it, especially the higher resolution data only available to the military. GPS 3 satellites will be more resistant to jamming, but the US military, but especially the US Navy, had better start teaching its officers a plan-B if GPS become unreliable. Many weapon systems may not target if GPS is unavailable. US Navy officers may need to channel their inner Zoltán Dani to destroy incoming missiles. Infantry officers would have it easier, but they should remember the lesson taught when engineers still used slide rules: always have a ballpark estimate ready to verify that the data is not completely wrong.
If your author was working for China, he would design a mini-sub with one mission, to locally jam GPS. It would be either partially or completely autonomous to eliminate a manned submarine's need to provide oxygen for its crew. It would be designed in a stealthy manner, especially with respect to the antenna that would extend above the surface of the water when it surfaced. It would not surface until an attack was imminent, only starting to jam GPS when it was almost too late to switch to plan-B. Even if it was noticed, it would only complicate things.
And the US should stop issuing security clearances to those born in China or Russia and revisit clearances already given. There have been many cases of Chinese nationals caught spying for mother China, but it's the ones we haven't caught that should give us pause.