One important reason is that they suddenly realized they had lost control over this unmanned submarine. In fact, Jiang Cheng's earlier guess was quite right, as this thing is powered by He energy. Although it malfunctioned and ended up in the hands of Flame Country.
However, because it was still operational, the United States could still monitor its movements, at least certain that Flame Country could not have opened the device's outer layer of Adamantium.
This is because they were confident that their developed Adamantium should be the hardest alloy in the world. Therefore, they dared to let Flame Country research it, knowing that without fully disassembling the unmanned submarine, they couldn't possibly understand its internal structure.
But a week ago, when they suddenly found they had lost contact with this thing, they became panic-stricken.
There are only two reasons that could lead to such a result.
