Navy submarines are confined spaces. There's not a whole lot to do outside work. One thing less sailors will be able to do is smoke.

A new policy, announced Thursday, bans smoking below decks on Navy submarines. The policy is to take effect no later than Dec. 31.

The Pentagon in 1994 banned smoking within all Defense Department buildings and workplaces. On a submarine, it's not possible to pop outside for a smoke, so the practice has continued inside in a recirculated-air environment.

The commander of the U.S. submarine force said the impetus behind the smoking ban is the health risk to nonsmokers from secondhand smoke.

"Our sailors are our most important asset to accomplishing our mission," said Vice Adm. John J. Donnelly. "Recent testing has proven that, despite our atmosphere purification technology, there are unacceptable levels of secondhand smoke in the atmosphere of a submerged submarine. The only way to eliminate risk to our nonsmoking sailors is to stop smoking aboard our submarines."

"Nicotine replacement therapy," including patches and gum, will be made available, the Navy said.

Chewing tobacco, it would seem, will continue to be allowed, although Capt. Mark Michaud, the submarine force Atlantic surgeon, said, "What we want to discourage is smokers turning to alternative methods of tobacco use such as chewing tobacco."

Smoking rates are higher in the military than in the civilian population. Part of that has to do with the stress of wartime duty.

The Institute of Medicine, the health arm of the National Academy of Sciences, found that in 2005, a third of active-duty military members smoked compared with a fifth of the U.S. adult population.

Smoking was studied on two Pearl Harbor-based attack submarines as part of an inquiry into minimizing exposure to secondhand smoke. The results were published in 2004 in Aviation, Space and Environmental Medicine.

The study looked at which designated smoking area on a submarine, fore or aft, minimized nonsmokers' exposure. The study found no significant differences from one area to the other for cotinine, the major metabolite of nicotine.

The study did find a "discernable difference" in tobacco smell for the forward smoking area because it was immediately below the crew's mess.

"The aroma of cigarette smoke permeated this space when sailors used the forward smoking area," the study said.

The aft smoking area was in the main lube oil bay, past the reactor compartment, but near some exercise equipment. Most of the sailors said they'd prefer a smoke-free environment, but would rather tolerate some smell while exercising rather than while eating.