One-third of the Pacific Fleet submarine force is getting underway “to assess warfighting readiness” as part of Exercise Agile Dagger 2021, the Navy said Thursday.

Submarines from Pearl Harbor, Bremerton, Wash., and San Diego are deploying on short notice “to demonstrate their readiness, agility, and lethality,” according to the U.S. Pacific Fleet submarine force headquartered in Hawaii.

Without the Navy saying so, the exercise is a message to China and Russia about the Navy’s ability to surge its submarines — a stealthy and key U.S. advantage over both potential adversaries. Nuclear-armed ballistic missile submarines are not taking part in the drill.

“The Pacific submarine force is always ready,” its commander, Rear Adm. Jeff Jablon, said in a release. “Exercise Agile Dagger 2021 allows us to test our capabilities and showcase our warfighters’ ability to rapidly deploy armed submarines into the Pacific.”

To underscore the “armed” part, the Navy released photos of crews loading a Mark 48 advanced capability torpedo onto the USS Columbia in Pearl Harbor on Wednesday — an activity the Navy rarely publicly reveals.

The Columbia is a Los Angeles-class attack submarine based in Hawaii. The USS Chicago, also a Los Angeles sub, and the newer Virginia-class USS Missouri out of Pearl Harbor are also among submarines that are part of the exercise. The Columbia and Missouri departed Thursday, while the Chicago left today.

A total of about 36 U.S. attack, guided missile and ballistic missiles submarines operate in the Pacific.

“Our submarine force ensures capabilities overmatch by sharpening warfighting capacity in this short-notice exercise,” Jablon said. “Our unparalleled key to success in undersea dominance is the U.S. Navy sailor. We have, and must continue to develop, the best trained sailors; so we must test our ability to load out weapons and supplies for extended combat operations, deploying to multiple locations in the Pacific.”

Exercise Agile Dagger 2021 “ensures the submarine force remains ready for global tasking to deliver a full range of undersea lethal effects,” the Navy said.

Cmdr. Cindy Fields, a spokeswoman for the Pacific sub force, said Agile Dagger in particular is aimed at honing skills in loading out weapons and supplies for extended combat operations.

Submarines can conduct anti-submarine warfare, anti-surface ship warfare, land strike with Tomahawk missiles, intelligence, surveillance, reconnaissance and early warning, special warfare capabilities, and strategic deterrence with nuclear-armed ballistic missiles submarines.