Sometime in 2021, Rhode Islanders will begin building mammoth submarines with enough firepower to decimate larger enemy countries and annihilate smaller ones.

The hope is that the destructive potential of these submarines will be so overwhelming that no country would even think of attacking the United States.

While these submarines will mean security for the nation, they will also mean hundreds of jobs for Rhode Islanders and hundreds of millions of dollars paid to companies that supply defense contractor General Dynamic Electric Boat, which operates submarine-building shipyards at Quonset Point in North Kingstown and in Groton, Conn.

This vision of military and manufacturing might took a step closer to reality recently when President Obama signed the bipartisan National Defense Authorization Act for 2014, a law that earmarks billions in defense spending that will be felt in the Ocean State’s economy.

The $632.8-billion measure authorized $1 billion to continue the planning and design of these new ballistic-missile submarines, which will replace the aging Ohio class.

The measure also includes:

• $5.8 billion to build two Virginia-class fast-attack submarines beginning this year, advanced-procurement funds to pave the way for two more Virginia-class subs beginning next year and support for a 10-ship contract being negotiated between the Navy and Electric Boat.

• $12.4 million for renovation and modernization of a building at the Naval War College in Newport.

• $6 million to build a facility that will house a full-motion flight simulator at Quonset State Airport, home of the Rhode Island Air National Guard’s 143rd Airlift Wing, to train crews on the C-130J Super Hercules transport plane.

The defense authorization act comes as a relief to area defense contractors and uniformed and civilian military personnel, some of whom face sharp reductions under a series of forced federal budget cuts called sequestration. The automatic sequestration cuts took effect because congressional negotiators had not agreed on a budget. But late last year, they struck a bargain, which Mr. Obama signed on Dec. 26, the same day that he signed the defense authorization act. The budget agreement repealed the sequestration cuts, replacing them with smaller, more flexible cuts to military spending.

Federal spending comes in a two-step process, first an authorization bill and then an appropriations bill. Congress is expected to approve the defense appropriations bill sometime this week. Until it is passed, changes could be made.

Sen. Jack Reed, the Rhode Island Democrat who is chairman of the Armed Services Subcommittee on Seapower, underscored the importance of defense spending to Rhode Island’s economy.

In 2012, the defense industry had an estimated $2.2-billion impact on the state’s $43.1-billion economy, a contribution of more than 5 percent, according to an October report from the Southeastern New England Defense Industry Alliance, an industry association.

Reed said an estimated 16,000 people work in the state’s defense industry, with an average yearly pay of $63,216, as of 2011. The average salary in the state is $45,702.

“These are good-paying jobs with good benefits,” he said.

Also, a substantial portion of those jobs are in manufacturing trades, which could be important to Rhode Island’s economic future, Reed said. “If we’re going to see a manufacturing renaissance, we have to keep these manufacturing skills alive.”

Along with those manufacturing skills, Rhode Island is a center of brain power when it comes to the nation’s defense, especially regarding the Navy. Aquidneck Island is home to the Naval War College and the Naval Undersea Warfare Center, a research and development arm of the service.

“Newport is the intellectual center of the Navy,” said Reed.

That’s why Congress approved $12.4 million for improvements to Hewitt Hall at the War College.

According to Lisa M. Woodbury Rama, a spokeswoman for Naval Station Newport, which encompasses the War College, the money will be used to update the building, which has been largely unchanged since it opened in the 1970s. Hewitt Hall is home to the Henry E. Eccles Library, which officials hope to transform into a “learning commons” with library and classroom functions along with information technology for online teaching, collaboration and meetings. The renovations are currently in design, and the Navy hopes to put the project out to bid late this year, Rama said.

The Naval Undersea Warfare Center employs 2,730 people, nearly three-quarters of whom are engineers and scientists, developing and improving systems that will be installed on the nation’s submarine fleet, according to Rear Adm. David M. Duryea, the commanding officer.

“We’re the lead for the submarine combat system program and the sonar program,” Duryea said, adding that the facility also works on periscope and imaging systems for submarines and unmanned undersea vehicles, also known as drone submarines.

Some of the money Congress allots for the Virginia-class and Ohio-replacement-class submarine will be spent at the Undersea Warfare Center, which doesn’t stop working once the initial design of a submarine class is finished.

“We’re installing, upgrading, modernizing the combat systems, imaging systems, electronic-warfare systems,” Duryea said.

As an example, the first incarnation of Virginia-class submarines included 12 vertical-launch tubes in the bow to launch Tomahawk cruise missiles. Virginias now under construction have replaced the 12 tubes with two Virginia Payload Tubes in the bow, each capable of launching six Tomahawks, but also other systems, such as drone submarines or drone aircraft. And design is under way for a Virginia Payload Module, a set of four Virginia Payload Tubes that will be installed in the aft section of a longer version of the Virginia-class design. The Virginia Payload Module will allow the fast-attack subs to take up the slack in cruise-missile capacity as the Navy’s guided-missile submarines – modified Ohio-class ballistic missile submarines – retire over the next two decades.

The facility is in the final stages of installing a $20-million apparatus that simulates a Virginia Payload Tube so that engineers can design and test the drones and other devices that will be launched from the submarines.

It also is helping other Navy branches and Electric Boat in the design of the Ohio-replacement class.

Duryea said that the Undersea Warfare Center spent $400 million in contracts for work by outside companies, of which $250 million was spent in Rhode Island. The center, teamed with local businesses, is developing expertise in submarine design, he said. “This is the center of excellence for undersea warfare.”

Of the 2,730 people employed by the center, 1,924 are from Rhode Island, 442 from Massachusetts and 200 from Connecticut. The center employs several hundred at smaller facilities in New York state, Florida and the Bahamas. Only 24 of its employees are uniformed military – 7 officers and 17 enlisted. The rest are civilians.

The defense authorization’s biggest immediate economic impact in Rhode Island will be from the $5.8 billion approved to build two Virginia-class submarines beginning this year.

Virginia-class submarines begin as large sections of each boat called supermodules, which are built at Electric Boat’s shipyard in Quonset Point. The supermodules then are shipped to EB’s shipyard in Groton, Conn., or to Newport News Shipbuilding in Virginia, where they are assembled into finished submarines.

“Everything begins at Quonset,” said Reed.

Electric Boat employs more than 12,000 people at all locations, according to company spokesman Robert A. Hamilton. That includes 2,767 at Quonset, of whom 2,436 are Rhode Islanders. The company has another 48 employees at an engineering office in Newport. It has 5,936 workers at its main shipyard in Groton, 987 from Rhode Island, and 2,956 at its engineering office in New London, Conn., 447 from Rhode Island.

The two Virginia-class vessels approved for this year, the advanced procurement for two more next year and support for a contract for 10 more ships means plenty of work for Rhode Islanders, Reed said. “That is not only jobs, but stability for the next two years and beyond.”

Beyond that, the Ohio-replacement class promises work for decades to come.

The Ohio class of ballistic-missile submarines – once known popularly as Trident subs – was conceived in the 1960s and designed in the 1970s, and individual subs went into service from 1984 to 1997. Their original lifespan of 30 years has been extended to 42.

Ballistic-missile submarines are part of a triad of nuclear-missile platforms – along with land-based silos and nuclear bombers – designed to deter an attack on the United States because an enemy would probably not be able to destroy all three systems, leaving the United States with the ability to launch a counterstrike.

“We’re looking at systems that have been vital parts of our deterrent, but they’re aging,” Reed said.

The plan is to build 12 of the new class of ballistic-missile submarines, each with 16 tubes capable of launching a single Trident II D5 nuclear missile.

“It’s the No. 1 priority in the Navy,” Reed said. “We have to maintain a smart nuclear deterrent.”

Of the three branches of the triad, submarine-based missiles are considered the least vulnerable to enemy attack.

Construction of the first sub in the replacement class is expected to begin in 2021, according to Hamilton. It should be delivered in 2028, shortly after the first Ohio-class ballistic-missile submarine is decommissioned.

The $6 million to be spent at the National Guard base at Quonset State Airport will build a 10,600-square-foot building to house a Lockheed Martin Hercules C-130J flight simulator, with the capacity to train 2,000 pilots a year, according to Master Sgt. Janeen Miller, spokeswoman for the 143rd Airlift Wing, based at Quonset.

The price of the simulator itself isn’t known yet, but Miller said it should be in operation by late next year.

Currently, crews from Quonset practice mostly by flying the aircraft, which leads to wear and tear on the planes, Miller said. Once the simulator is installed, they’ll be able to shift about half of their training to the simulator.

Currently, local crews go once a year to Keesler Air Force Base in Mississippi for training that can be done only on a simulator, she said. Once Quonset has a simulator, crews from other parts of the country will come here to train.