Retired Navy Cmdr. Delos S. Calkins Jr., 44, a former nuclear submarine weapons officer and a veteran of the Vietnam conflict, died of a pulmonary embolism Saturday at the National Naval Medical Center in Bethesda.

After earning a bachelor's degree in naval engineering from the Naval Academy at Annapolis in 1958, Cmdr. Calkins served aboard surface ships and conventional submarines.

In 1963, he transferred to the U.S.S. Daniel Boone, a fleet ballistic missile submarine, as Polaris weapons officer.

From 1969 to 1972, he served as executive officer of the U.S.S. Thomaston, off the coast of Vietnam in the South China Sea.

He also served in this area with the Navy's old Special Projects Office, now the Strategic Systems Project Office, where he assisted in the development of improved Polaris and subsequent fleet ballistic missile weapons programs.

Cmdr. Calkins was assistant head of the Fire Control and Guidance Branch of the Strategic Systems Project Office when he retired in January.

In recent weeks, he had been working as a staff engineer for the local offices of EG & G Inc., a research company.

Cmdr. Calkins was born in New York City. He lived in Fairfax.

Survivors include his wife, Dorothy E., and a son, John D., both of Fairfax; his parents, retired Army Lt. Col. Delos S. Sr. and Mrs. Calkins of Miami; a brother, Alan B., of Gainesville, Fla., and a sister, Harriet Williams of Coral Gables, Fla.

The family suggests that expressions of sympathy be in the form of contributions to the American Heart Association.