Article author Richard Chirgwin is either a stooge or incompetent (or this is just cljckspam). Here's why:
What Greenwald wrote is, "“Speargun” involved the covert installation of 'cable access' equipment, which appears to refer to surveillance of the country’s main undersea cable link, the Southern Cross cable."
In no way does this include Greenwald claiming that the undersea portion of the cable link was accessed. It could be done the same way splitters feed Room 641A (Google it or see video.pbs.org/video/2365249828 ...)
Not to mention that other commenters have pointed out that the US has assets (USS Jimmy Carter) designed specifically to tap undersea cables.