"I think it will fit very well, especially considering his experience with the military, and the military and government presence in this area," said Kevin Brown, a deacon at Holy Trinity Church in Glen Burnie.
Archbishop William D. Borders, a former military chaplain himself, said he had worked with O'Brien in the past.
"He's a scholar, understands the church and knows how to delegate," the retired archbishop said. "Incidentally, for a bishop, that's very important."
However, "in the military, everything is an order," Borders said. "You give orders. In the priesthood and in the diocese, everything is volunteer."
O'Brien spent much of his time in the military archdiocese on the road, visiting about 1.5 million servicemen and servicewomen at bases and in battle zones. He will have a similar schedule as archbishop of Baltimore, at least at first.
After the installation, O'Brien said he plans to travel the diocese, to see parishes in Western Maryland first and then the urban churches in Baltimore and elsewhere.
That might be the only similarity between his previous and future roles, however. O'Brien had no cathedrals while he led the Archdiocese of Military Services - now he has two.
"In one sense, it's more containable," O'Brien said. "To try to get your arms around a congregation of 1.5 million is rather daunting."
"But when we have parishes and institutions of Catholic charities and education, I know I can get to know the people and get to know the situation much more readily and be present to them much more frequently."
And he'll travel to the Vatican next year to receive his pallium - a woolen band that signifies his position as the leader of a "metropolitan," a diocese with largely symbolic authority over dioceses such as Wilmington, Del., Arlington, Va., and Wheeling, W.Va.
O'Brien is the only current bishop to have led two seminaries: St. Joseph's Seminary in New York and the Pontifical North American College in Rome.
As archbishop of Baltimore, he is chancellor of the two seminaries within the Archdiocese of Baltimore: St. Mary's Seminary in Roland Park and Mount St. Mary's in Emmitsburg. O'Brien said Keeler had stressed vocations, with more than 30 men accepted during the past three academic years.
"I'm going to continue that," O'Brien said. "I'm going to take great interest in both seminaries. To the extent that they will ask for my opinion and invite me to join in their prayer life, I will, and also I have some oversight responsibilities as well."
"I hope to lend a hand in making some suggestions, maybe, that will improve the formation of priests in the archdiocese," he said.
The Rev. Thomas R. Hurst, the president-rector of St. Mary's Seminary and University in Roland Park, said he looks forward to working with O'Brien.
The new archbishop will live in a North Baltimore residence owned by the Sulpicians, the order of priests who run St. Mary's Seminary.
Hurst says he got to know O'Brien while serving as rector of Theological College, the seminary at Catholic University of America, which once housed the offices of the Archdiocese of Military Services.
While at St. Joseph's and the North American College, "he was a wonderful pastoral presence to the students, as well as being the model of a man of the church," Hurst said. O'Brien also led the Vatican-driven visitation of seminaries last year.
The two would sometimes share a meal, and O'Brien occasionally celebrated Mass for the seminary.
Hurst said O'Brien took his priestly duties seriously, which was evident in the way he interacted with military personnel, their spouses and children, as well as with chaplains.
"He's a man of deep pastoral concern," the rector said.
The Rev. Daniel R. Goulet, a newly ordained priest who was co-sponsored by the archdioceses of Baltimore and Military Services, met with O'Brien several times during his seminary training.
"He has a tremendous love for soldiers and family members, as well," Goulet said. "I found him to be a very caring leader and a very strong leader, as well."
See a video at baltimoresun.com/obrien
Archdiocese-run Catholic schools will be closed today.
The installation ceremony will be broadcast live on the Catholic cable channel, EWTN, as well as some other local television stations and their Web sites.