The 30th Air Defense Artillery Brigade at Fort Sill, Oklahoma, will have to wait a little longer. Army First Lieutenant Ella Ellis remains in Maine to play professional basketball.

Three days before the Red Claws open their seventh NBA Development League season, they trimmed their roster from 16 to 12, and among the final dozen is a 6-foot-7 graduate of West Point whose last collegiate game was more than two years ago.

“I’ve always had the dream of playing in the NBA,” said Ellis, a first-generation American whose parents are from Jamaica. “That’s something I tell my friends every day.”

Of course, there’s still no guarantee Ellis will suit up for the Red Claws Thursday night in Westchester, New York. Only 10 players will be active for that game, along with any players the parent Celtics send down from Boston.

“He’s played his way into the early roster,” said Red Claws Coach Scott Morrison before Monday’s practice. “But as of now, he’d be down there on the depth chart and probably wouldn’t be active, if we’re healthy.”

Still, there’s a chance. The Red Claws picked Ellis in the second round of the D-League draft last month after seeing old game footage and speaking with his coaches at Army and with the all-Army and all-Armed Forces teams on which he’s played since graduating in May 2013 with a degree in information technology.

“We all wanted to take him,” Morrison said. “We all wanted to see what he could do.”

Ellis scored five points on 2-of-6 shooting in Sunday night’s intrasquad scrimmage. He had an assist and two rebounds and made 1-of-4 3-point attempts.

“I think the thing that sticks out so well has nothing to do with his ability as a player,” said his coach at Army, Zach Spiker. “He’s a tremendous worker. He’s driven. You combine his skills with his personality, and it’s impossible not to want the best for him.”

Red Claws General Manager Dave Lewin, the Celtics’ director of scouting, remembered Ellis from his time at Army, where he became the only cadet in team history to rack up 1,500 points, 450 rebounds, 150 assists and 40 blocked shots.

“He had a terrific senior season,” Lewin wrote in an email. “He was never an NBA prospect but when I saw his name pop up on the draft list I knew he was someone we would want to consider drafting.”

The list of West Point graduates who have gone on to play in the NBA is short. It consists of one name.

Mike Silliman played for Bobby Knight at Army, became captain of the 1968 U.S. Olympic basketball team and had a brief pro career with the New York Knicks and Buffalo Braves.

Ellis, 24, grew up in Houston in a household that stressed the value of education. He ranked 24th in his high school class of more than 600 and played on an AAU team with Tim Frazier, the star of last season’s Red Claws team and the D-League MVP who now plays for the NBA’s Portland Trail Blazers.

“I was a senior when he was a junior,” Ellis said. “He was starting at point guard and I started at the small forward position.”

They still keep in touch, as does former Indiana Pacers standout Reggie Miller, who provided color commentary for several Army-Navy games broadcast through Ellis’ career.

Miller comes from a military family and struck up a friendship with Ellis. He tweeted congratulations the day the Red Claws drafted Ellis.

“He’s kind of been tracking me over the past two years, which is really cool,” Ellis said. “My mother went back to college after I graduated. She got her associates in accounting. He tweeted, ‘Hey, let your mom know I’m really proud of her. It just shows that education is good at any age.’ ”

Upon graduation from West Point, Ellis faced a five-year commitment to the Army. After two years, he can apply for early release if he has a professional opportunity. The NFL has a few West Pointers who took that route, including Pittsburgh Steelers offensive lineman Alejandro Villanueva.

That’s why Ellis didn’t toss his name into the D-League hat until this year.

“I knew it was going to be kind of a long shot having to wait another year,” he said, “but at the end of the day, I have to do right by the Army and I wanted to do right by any organization that drafted me. So I waited another year and entered my name.”

The 12 players scheduled to open the season for the Red Claws come from four pools: Returners Andre Stringer, Omari Johnson and Ralph Sampson III; Celtics affiliated players (who went to training camp with Boston) Corey Walden, Coty Clarke, Malcolm Miller and Levi Randolph; D-League draft picks Kevin Young, Karrington Ward and Ellis, and tryout invitees Coron Williams and Curtis Washington.

“I think I’ve taken the most improbable road to get where I am right now,” Ellis said. “Whatever happens after this, I can’t be disappointed because I’ve had many opportunities and this is obviously one of them.”