Noah Song, a Navy officer, is allowed to continue his pitching career. And the Red Sox’ decision to let him walk could backfire.

Noah Song fell to the Red Sox in the fourth round of the 2019 draft because of his pending military service.Phil Hoffmann

FORT MYERS, Fla. — The Red Sox fired Dave Dombrowski in 2019 and hired Chaim Bloom a few months later because ownership changed its philosophy and wanted a more sustainable and economical method of building the roster.

Dombrowski’s win-now approach of trading prospects for stars and signing high-priced free agents was replaced by Bloom’s system of carefully working the margins to build a wider talent base.

So it was mildly amusing in December when the Phillies, now led by Dombrowski, selected righthander Noah Song from the Sox in the Rule 5 Draft of veteran minor leaguers.

Song, while a very talented pitcher, hadn’t been in a game since 2019 because he was serving in the Navy.

But Dombrowski was smiling widely when the selection of Song was announced on the final day of the Winter Meetings in San Diego.

“We thought we had nothing to lose,” he said.

Now they have everything to gain. The Phillies announced Wednesday that Song has been transferred from active duty to selected reserves and given permission to continue his baseball career. He will report to Phillies camp in Clearwater on Thursday.

It’s a potentially embarrassing development for the Red Sox, who may have let a future ace slip away to Dealer Dave.

Song, now 25, was a first-round talent at Navy who fell to the Sox in the fourth round of the 2019 amateur draft because of his pending military commitment. Dombrowski was president of baseball operations at the time.

The Sox selected him and were immediately entranced by his abilities. Song had a 1.07 ERA in seven starts for Lowell in rookie ball then was terrific for Team USA in the Premier 12 Olympic qualifying tournament that summer against experienced professional players.

That was it. Song disappeared into the Navy and helicopter flight school. His name popped up from time to time over three years, but only in reference to his being unable to get permission from the Navy to return to baseball, something several football players from service academies had been granted.

Did Dombrowski get the last laugh on his old team?Jim Davis/Globe Staff

The Sox did all they could to help but the Navy didn’t budge for years. Then Song went to the Phillies and it happened 11 weeks later.

That wasn’t entirely unexpected, I’m told. But the Sox still didn’t want to tie up a 40-man roster spot on a pitcher who had been idle for three years.

Bloom didn’t seem too concerned about what could happen in December when Song was selected.

“You don’t ever want to lose anybody,” he said. “Given his situation, we felt that when he returns from his commitment, being on the 40-man roster would not be an ideal situation to have. That’s a risk we were willing to take.”

The Sox had the option of putting Song on the 40-man roster and placing him on the military list, which would have removed his Rule 5 eligibility with the caveat that he would have had to return to the 40-man once his commitment ended.

They took a chance and Dombrowski called them on it. Bloom made a similar move when he took Garrett Whitlock from the Yankees in the 2020 Rule 5 Draft while he was recovering from Tommy John surgery.

This time, for the sake of assorted fringy big leaguers, the Sox lost one of their best prospects.

Under Rule 5 rules, the Phillies have to keep Song on the 26-man roster once the season starts. If not, he could be traded or placed on waivers.

If Song clears waivers, he must then be offered back to the Red Sox.

There’s a chance this works out handsomely for the Sox. Perhaps Song doesn’t make the Phillies and the Sox get him back now free of his military commitment and need to be on the 40-man roster.

But a deep team like the Phillies could retain Song on the 26-man roster and use him in low-leverage spots as he builds back up. That’s not a high price to pay for a first-round talent.

The Red Sox lost Song to the Phillies.Kiyoshi Ota/Getty Images

And while he would never admit it, Dombrowski would love to take advantage of the Sox after they unjustly fired him only 10½ months after winning the World Series.

When last he pitched, Song featured a four-seam fastball that hit 99 miles per hour, a good slider, and a changeup that showed potential.

Dombrowski thought Song was the best player available in the draft that season.

Now Song will get a chance to prove it and the Red Sox can only watch.