Washington Cardinal Donald W. Wuerl and Archbishop Timothy P. Broglio, who heads the Washington-based Archdiocese for the Military Services, both issued brief statements offering prayers for the victims and their families.
The shooter was identified as Aaron Alexis, 34, who became the 13th victim when he died in a gun battle with police at the naval office building in the nation's capital. At first, law enforcement authorities thought there was a second shooter, but by the end of the day confirmed Alexis was the only gunman.
According to news reports, Alexis was a former Navy reservist who received a "general discharge" from the service and had moved to the Washington area from Texas about a year ago. He worked for a military contractor and had security clearance at the Navy Yard.
Archbishop Broglio said the "terrible loss of life" shocked and saddened him, particularly as it occurred at a familiar place where he has often visited and celebrated the Eucharist.
"Somehow we must restore the notion of respect for life into the fabric of the nation," he said in a statement. "When the uniqueness of the human person created in the image and likeness of God is universally recognized, the possibility of a mass shooting is more remote."
The Sept. 16 attack unfolded shortly before 8:30 a.m. (Eastern time) in one of several large buildings at the Navy Yard. About 3,000 people work at the facility, which is the headquarters for Naval Sea Systems Command. It is the largest of the Navy's five system commands.
Some witnesses told of encountering a gunman in a hallway; others described someone shooting from an upper-level overlook area into a cafeteria below.
Cardinal Wuerl in his statement offered his prayers for the victims, their families and friends, as well as for the emergency responders on the scene. The injured included a police officer.
He noted that "while many facts are still unknown, our most powerful tool right now is prayer," adding that the church always calls people to prayer, particularly at times of crisis. "It is what we do best because it is what the Lord asks us to do."
As he opened a news conference on recovery from the banking crisis, President Barack Obama also extended his prayers and observed that the attack targeted military and civilian personnel at a military installation.
"These are men and women who were going to work, doing their job, protecting all of us," he said. "They're patriots, and they know the dangers of serving abroad -- but today, they faced unimaginable violence that they wouldn't have expected here at home."
He particularly offered his gratitude to the Navy and law enforcement authorities and to the doctors who responded "with skill and bravery."
Among the religious entities offering prayers, the Washington National Cathedral, administered by the Episcopal Church, announced that its noon Eucharist service and the choral evensong service would include special prayers for victims, responders and the Navy community.
The cathedral's dean, the Rev. Gary Hall, in a statement offered the cathedral's space and its ministries "to all who seek consolation and refuge from this loss."