Mr. Slutman was told that his son was one of three Marines killed on Monday in Afghanistan when a roadside bomb exploded near their military convoy. An Afghan contractor and several civilians were injured.

The death of Firefighter Slutman, 43, highlighted a tradition of firefighters serving dual roles in the military. Currently, 73 New York Fire Department personnel are on extended military orders in branches of the United States Armed Forces, serving around the world. The department said 1,425 of its members are military reservists or veterans.

A 15-year veteran in the New York City Fire Department, Firefighter Slutman served at Ladder Company 27 in the South Bronx before his most recent deployment, and had won a Fire Chief’s Association Memorial Medal in 2014 for rescuing a woman from a burning apartment.

On Tuesday, he was remembered by mayor Bill DeBlasio as an “American hero, a New York hero.”

His friends said they knew other firefighters who, like Mr. Slutman, felt the need to serve more, particularly after Sept. 11.

“Our job already is pretty dangerous, so for anybody to take on kind of a second career that would be as dangerous, or even more, is slightly mind-boggling,” said Michael Seilhamer, who said he worked with Mr. Slutman as a volunteer firefighter in Maryland and rented a beach house with him in Delaware for years.