The Navy has uncovered no evidence of a cyberattack in two separate deadly collisions involving two Navy destroyers this summer, Adm. John Richardson, the chief of naval operations, said Wednesday.

Richardson said the service has given an "amazing amount of attention" to potential cyberattacks and is still investigating the possibility that some type of intrusion could have played a part in the June and August collisions of the USS John S. McCain and USS Fitzgerald in the Pacific, which killed a total of 17 sailors.

But he also discounted what he called a thread of public speculation on a cyber angle in incidents that have sent the Navy reeling and triggered a fleet-wide review of training.

"We'll continue to look deeper and deeper but I just want to assure you that to date there's been nothing that we've found to point to that," he said during a Navy all-hands call streamed on Facebook Live.

Both the McCain and Fitzgerald collided at night with merchant ships, causing flooding that killed crew and extensive damage that put the destroyers out of duty.