The vulnerability of deep-sea cables during conflicts is raising global security concerns, leading 17 nations to increase defense collaboration, though China and the US are notably absent.

The vulnerability of submarine cables during conflicts has made seabed infrastructure a fresh concern for global communication and maritime safety, prompting 17 Asian and European nations to step up collaboration on defence strategies in recent months. But the two largest marine powers, China and the United States, were not among those countries. From the blow-up of the Nord Stream pipeline to the development of new technology such as China’s deep-sea cable cutter, the seabed has become the...