Groton — Inside the future submarine South Dakota, workers crouched under piping and into tight spaces. They waited for a colleague to pass through a corridor before they could make their way.

Sparks flew in the torpedo room as a male employee finished up some welding. Outside a berthing area, a female employee was drilling. There was already a coffee machine in the officer wardroom. Inside the control room — essentially the brain of the submarine — stainless steel covers protect screens that will display sonar and fire control information.

About 550 Electric Boat employees are assigned to work on the South Dakota. On Thursday afternoon, about 300 of them were spread out within and around the submarine, which the company is expected to deliver to the Navy by mid-2018.

The South Dakota, which is about 85 percent complete, is one of five future Virginia-class attack submarines in various phases of construction at the busy Groton shipyard. These boats, along with an upcoming fleet of ballistic-missile submarines, represent one of the most complex submarine-building eras since the 1970s, Rear Adm. Bill Merz, director of undersea warfare, said during a recent lecture in Groton.

In the 1970s, EB, one of only two private shipyards that build subs for the U.S. Navy, was turning out a high rate of Los Angeles-class submarines while also building Trident ballistic-missile submarines. From 1974-84, 20 Los Angeles-class subs and six Ohio class, all built at EB, were christened.

"We're kind of entering that era again. Two full production lines of two different classes of ships," said Will Lennon, vice president of the Columbia program at EB. "We want to make sure that we're prepared for that."

In addition to the South Dakota, the Vermont, Oregon, Hyman G. Rickover and Iowa are under construction at EB. The government contracts also are keeping 3,700 employees busy in Quonset, R.I., where all the modules are fabricated. Four additional Virginia-class subs are being built at Newport News Shipbuilding in Virginia.

The two companies have been building two Virginia-class attack submarines a year since 2011. Starting in 2019, the Virginia boats will be built with a Virginia Payload Module, an added 80- to 85-foot-long section intended to provide additional Tomahawk missile capacity. The added section will result in a roughly 25 percent increase in work. EB also is gearing up to build the lead ship in the Columbia program, a new fleet of 12 ballistic-missile submarines that will carry 70 percent of the country's active nuclear arsenal.

"Columbia being a strategic deterrent submarine, it's been 25 years or so since we've been in that build plan of building a strategic deterrent," Lennon said.

Many employees who worked on the Ohio-class submarines, which the Columbia submarines are replacing, are nearing retirement, and EB is restarting the supply chain tied to building strategic deterrent submarines.

"We're bringing them back up to speed with a whole new set of requirements and capabilities to support," Lennon said.

It takes about five and a half years to build a Virginia submarine. It will take about seven years to build the second through 12th Columbia submarines, which are two-and-a-half times the size of Virginia subs. The lead ship in a new class of submarines takes longer to build.

With the two-per-year build rate for Virginia submarines, plus proposals to build three of those submarines in some years, and the Columbia submarines yet to be built, there's a sense in the shipyard that the frenzied pace of work isn't going to let up anytime soon.

So far this year, more than 500 employees have been hired to work in the shipyard alone. By 2030, the company expects to have a workforce of 18,000, compared to the 15,600 it has now. In actuality, that will require hiring between 15,000 and 20,000 people, accounting for both new positions and normal attrition. Right now, the focus is on hiring workers — including welders, machinists and pipefitters — for the shipyard.

Finding and training that number of new employees is no small task. EB has worked with the region's technical high schools, community colleges and local workforce development organizations to put in place training programs for various trade specialties. The idea is to create a pipeline that will turn out high-skilled workers in the quantities that EB needs. The company also reconstituted its internal apprenticeship programs tied to its two principal unions.

'A pretty empty place'

U.S. Navy submarines cost billions to build. Federal lawmakers, especially those whose districts stand to benefit from defense jobs, have shown a renewed interest in these war machines and their role in ensuring national security following a drop in submarine production after the Cold War and the prominence of other military policies in the period after Sept. 11.

In December 2006, shortly after U.S. Rep. Joe Courtney, D-2nd District, got elected to Congress, he met with John Casey, then the president of EB.

"At that point, they were still limping along at one (Virginia submarine) a year. ... It was a pretty empty place in terms of number of boats that were physically there," Courtney said. And the company had announced a month earlier that it would be cutting 1,000 jobs the following year.

Fast forward to today, Courtney said, with five boats in the yard, a "very sizeable" backlog, and lawmakers giving preliminary approval to plans to build up to 13 Virginia submarines from 2019 to 2023.

"It's night and day," Courtney said.

Going forward, lawmakers will debate how to pay for the Navy's new goal of 355 ships, including more submarines, and other military programs, as well as spending on an array of nondefense programs and nondiscretionary portions of the federal budget, such as Social Security and Medicare. There likely will be heated negotiations about the Budget Control Act spending caps for the defense and nondefense parts of the discretionary budget. Since the November 2016 presidential election, officials have increasingly called for removing or raising the limits on defense spending.

j.bergman@theday.com