NAPLES, Italy — Smoking will be banned on submarines throughout the fleet by the end of the year, the Navy announced this week. The move doesn’t go into effect immediately because the Navy wants to give crewmembers enough time to quit smoking if they choose to do so.

“Submarine commanders have until December 31st to have their crews go through smoking cessation programs,” said Lt. Cmdr. Mark Jones, a spokesman for Submarine Forces. “If a commanding officer on a sub feels they can go smoke-free before December 31st, that’s encouraged, but December 31 is the deadline.”

The ban was driven by information from a Navy study completed last year on secondhand smoke in underway submarines. The yearlong study included testing on nine submarines including at least one from each class in the fleet.

The study has not been released publicly because it is still being assembled by the Navy’s Bureau of Medicine in Bethesda, Md., Jones said. Leaders were briefed on the findings.

“Recent testing has proven that, despite our atmosphere purification technology, there are unacceptable levels of secondhand smoke in the atmosphere of a submerged submarine,” Vice Adm. John J. Donnelly, commander of Submarine Force, Atlantic, said in a statement Thursday. “The only way to eliminate risk to our nonsmoking sailors is to stop smoking aboard our submarines.”

Secondhand smoke “has been linked to an increased risk for heart disease and lung cancer among adult nonsmokers,” according to the U.S. Surgeon General. A report on the agency Web site says: “Separating smokers from nonsmokers, cleaning the air and ventilating buildings cannot eliminate exposure.”

The new policy allows individual commanders to decide if crewmembers can smoke on deck while their subs are above water.

Jones said about 40 percent of submariners smoke. Though smokeless tobacco isn’t banned, its use is highly discouraged.

A ready supply of nicotine patches and gum will be stocked to help smokers deal with the ban while they’re underway, officials said.