"Although the traditional public commissioning ceremony was canceled due to public health safety and restrictions of large public gatherings, the Navy commissioned USS Delaware administratively and transitioned the ship to normal operations," the announcement said.

Jill Biden, the wife of Democratic presidential candidate Joe Biden, is the sub's designated "sponsor"; its construction began while her husband, a former US senator from Delaware, was serving as the US vice president.

In a statement, she congratulated all involved in the complex process of building a nuclear submarine longer than a football field.

"I know this submarine and her crew of courageous sailors will carry the steadfast strength of my home state wherever they go," she said.

The Delaware is a Virginia-class sub, the latest generation of cruise missile fast-attack submarines in the US fleet.

The Delaware's nuclear propulsion system means it can go 30 years without refueling, the navy's statement said.

The sub is 377 feet (115 meters) long, can dive to depths of 800 feet and operate submerged at speeds of 25 knots (45 kph).

It is armed with medium-range ballistic missiles and is capable not only of attack missions but also surveillance, intelligence and reconnaissance. It can also deliver special operations forces to target zones.

The US fleet of attack submarines is the world's largest, with 56 subs.

The coronavirus pandemic has had far-reaching impact on the US military, limiting troop movements around the world and, notably, prompting the evacuation of the aircraft carrier USS Roosevelt after it docked in Guam with more than 100 crew members suffering from COVID-19.

To lessen the risk of contamination in a space as closed as a submarine, which may spend weeks underwater, crews are isolated together for a two-week quarantine before embarking.

A second crew is also isolated for two weeks in case it is needed to replace the first crew.