Cmdr. William Patterson inside the control room of the fast-attack submarine U.S.S. Hawaii, docked at Yokosuka Naval Base, Japan, on Thursday. “I would take this ship and this crew against any submarine in the world,” Patterson said. (Anna Fifield/The Washington Post)

The whole idea of the U.S. Navy’s stealthy, fast-attack nuclear submarines is that they can go undetected, but when the USS Hawaii docked here, its commanders went out of their way to draw attention to the $2 billion vessel.

Its patched-up black tower looming out of the harbor’s waters, the Virginia-class nuclear sub showed up to reassure the uneasy Japanese that American power is still on their side, and still a force to be reckoned with.

“The Hawaii represents the best submarine in the world,” said Rear Adm. Stuart Munsch, who is in charge of all American submarines between the International Date Line and the Red Sea. “We’re bringing our best out here to our most important region.”

Munsch, together with Cmdr. William Patterson, the Hawaii’s commanding officer, showed two top Japanese admirals around the boat while it was tied up here last week and took a small group of reporters on a rare tour.

The apparent idea was to make a very visible impression at a time when U.S. allies in Asia — especially Japan, which is embroiled in a territorial dispute with China over a group of remote islands — worry that the Pentagon has turned its attention elsewhere.

Fast-attack submarine U.S.S. Hawaii, docked at Yokosuka Naval Base, Japan, on Thursday. (Anna Fifield/The Washington Post)

“The United States’ capability used to be big and present on land but has increasingly been moved to the sea or back to the U.S.,” said Scott Harold, a political scientist at the Rand Corp .

“Our allies don’t see us as much anymore, so they don’t feel as secure anymore. We can remind them, as well as our potential adversaries that might threaten us, that we are there,” he said.

This message of reassurance is especially important at a time when — despite the rhetoric about a “pivot” to Asia — the United States remains overwhelmingly focused on the Middle East. But raising the Hawaii and showing off its features also serves as a reminder to China and North Korea that the United States remains a formidable force at sea.

To underline the point, the Navy invited the news media and other guests aboard for a look-see. The takeaway? Nuclear subs may be jaw-droppingly high-tech, but not even their most ardent proponent would suggest that these beasts were made for comfort.

Just ask Sam Shorts, the ­6-foot-8 supply officer on the Hawaii, who knows all the spots on board where he can stand up straight. Most of them are small spaces where his head can squeeze between a light bulb and some metal pipes.

As for the bunks, squeezed six to a cell-like room with barely 30 inches between the mattress and the bed above, Shorts estimates that they’re 6.5-feet long.

Still, he’s not complaining. “I jumped at the chance to serve on a submarine,” said Shorts, who was wearing the Navy’s mystifying blue camouflage uniform (wouldn’t sailors want to be seen in the water?), in the wardroom.

Although China is putting huge efforts into increasing its submarine fleet, and even cash-strapped North Korea likes to show photos of Kim Jong Un atop a Soviet-era sub, the U.S. boats are in a league of their own.

“I would take this ship and this crew against any submarine in the world,” Patterson said.

The Hawaii is a 377-foot stealth boat that can carry 150-plus crew members, 20 torpedoes and a dozen Tomahawk cruise missiles. One of 10 in its class, it is capable of launching strikes in the sea and onto land, conducting clandestine missions and launching SEAL special forces into the water — and getting them back again. Based at Pearl Harbor, the Hawaii patrols the Western Pacific, usually undetected.

The Navy has used its subs to send public messages before. During a tense standoff between China and the Philippines over the disputed Scarborough Shoal in 2012, the U.S. Navy surfaced another Virginia-class submarine in the area to make sure the Chinese knew it was there.

“It was a show of force in response to bad behavior,” said Patrick Cronin, an Asia expert at the Center for a New American Security . The visit of the Hawaii here, he said, “is not the same as the Scarborough Shoal, but the U.S. is taking a beating for looking weak and impotent and also for not properly resourcing the pivot, backing up our allies.”

There was widespread consternation in Japan and South Korea last year when President Obama threatened to launch airstrikes on Syria but then backed away from them. Some in Japan fear that the U.S. declaration to support its ally in a conflict with China might prove similarly hollow. So the Hawaii’s arrival would have been especially welcome.

Its job is not simply to threaten or unleash destructive power. Modern subs have advanced electronic sensors that collect intelligence by locating radars, missile batteries and command sites, as well as monitoring communications and tracking ship movements.

“One of the reasons we send them into China’s exclusive economic zone is to try to find out what they’re making and what they’re doing,” Cronin said.

Showing off the unique features of the Virginia class in the Hawaii’s control room, a large (for a submarine) space aglow with lights, the commander said the biggest difference was the shift to electronics from mechanical systems.

“It’s all about the periscope,” Patterson said, holding a joystick that looked like something a video game player might use, swinging the camera around to show people gathered on the pier outside.

The addition of an infrared camera also has been revolutionary, giving the crew the same clear picture at all hours.

“SEALs talk about ‘owning the night’ because of the technology they have,” Munsch said. “This is our equivalent — we own the night at sea.”

In peacetime, he said, “submarines add certainty. In combat, we take this same capability to sow uncertainty in the minds of the enemy. They don’t know where we are, or when we will strike.”