Groton — After serving aboard the USS Helena (SSN-725) and USS Chicago (SSN-721), two of the Navy's oldest submarines still in service, Lt. Cmdr. Reginald Preston thought his next set of orders would be to some "shiny" Virginia-class attack submarine.

Instead, in a perverse sense of humor, he joked, the Navy sent him to the oldest submarine "still on the decks."

For the past two years, Preston, 37, originally from Lyman, Neb., has been the officer in charge of the Historic Ship Nautilus, the first nuclear-powered submarine, and director of the Submarine Force Museum in Groton.

"There's not a submarine officer among us that doesn't enjoy a challenge and I'm no different," he said Tuesday at the museum during a change of charge ceremony during which he was relieved by Lt. Cmdr. Bradley Boyd.

But, keeping the original, nuclear military hardware, personally signed by Harry S. Truman and still classified, in perfect condition "has been a daunting task best appreciated by all of those who have come before me," Preston said.

Dressed in his dress blue uniform with an array of medals pinned to his chest, Preston spent much of his remarks thanking his family, some of whom were watching the ceremony via live video on Facebook, and those he's worked with. At one point, he asked his crew to stand for recognition, and got choked up while highlighting their work.

Despite the Nautilus being a decommissioned submarine, "you have to do a lot of what you do on a regular submarine with a quarter of the crew," such as maintaining watch duty rotations 24 hours a day, 365 days a year, said retired Rear Adm. Samuel J. Cox, director of the Naval History and Heritage Command.

That adds complexity to the job, which is unlike any other in the Navy, Cox said. "There's no cookbook for how to do this. No schooling," he added.

When Preston came to the job in April 2016, major maintenance for the Nautilus had been deferred for many years, and the Navy was faced with a big bill to preserve the ship for another 30 years.

"For the Navy to go to Congress and say 'I need multi-million dollars in order to keep a museum ship afloat' at a time when we were challenged to keep operational units underway was a very difficult thing to sell," said Cox, who tasked Preston with preserving the Nautilus "at far less cost."

Preston came up with a new maintenance plan that will save the Navy $104 million over 30 years, Cox said.

Coincidentally, Wednesday marks the 63rd anniversary of the Nautilus' commissioning, when its first commanding officer, Cmdr. Eugene P. Wilkinson, uttered the historic radio message, "Underway on nuclear power."

Today, the submarine "represents a visible link between naval history and the submarine force of tomorrow, but she only does so through the stewardship of leaders like Reg," said Rear Adm. James Pitts, head of the Undersea Warfighting Development Center in Groton.

Preston, who lives in Pawcatuck with his wife, Katey, and two daughters, won't be straying far. His next assignment is Director of Submarine On-Board Training at the Naval Submarine Base.

Boyd, the new officer in charge, who joked that he too has served on some old submarines, said he was immediately inundated with questions once he got the new job such as why there even needs to be a museum to begin with.

The ship and the museum are "essential to successful community engagement and the public's perception of the submarine force, naval nuclear propulsion and the Navy," Boyd said.  "... I have one of the most unique jobs in the Navy and a staff and crew second to none."

Boyd, 36, lives in Groton with his wife, Shannon, and their two children.

j.bergman@theday.com