KINGS BAY NAVAL SUBMARINE BASE, Ga. -- Aboard the submarine USS Florida, there's no e-mail or phone, no breaks for sunshine or fresh air. For many Navy sailors serving 90-day tours in cramped quarters underwater, one of the few creature comforts has been smoke breaks below decks around a butt bucket in the machine room.

By New Year's Eve, sailors will have to kick the habit.

In early April, the Navy ordered its fleet of 71 submarines to snuff out smoking onboard by the end of 2010 -- closing one of the last loopholes in an indoor smoking ban the U.S. military imposed in 1994.

The change means an estimated 5,200 smokers in the submarine fleet will have to pretty much quit a habit that for some is a pack a day, while for others is an occasional cigar. Those who need to stop expect a rough maiden voyage.

"You're going to have some very, very disgruntled sailors," said Petty Officer 3rd Class Cedric Dickinson, a cook aboard the Florida who's already cutting back from a pack-a-day to four cigarettes. "Everyone's going to be on edge."

The pending smoking ban was announced 16 years after the military extinguished tobacco smoke in most other indoor areas, from base office buildings to Air Force hangars, Army tanks and below decks on Navy surface ships.

The Navy made an exception for submarines. Sailors spend up to three months on undersea patrols without shore leave or even surfacing for sunlight.

Privacy is minimal and space so limited that sailors wait in line for showers, a seat in the mess hall for meals and cigarette breaks. On the Florida, only three at a time can light up while other smokers wait their turn.

If the Navy has its way, another potentially stressful change will be coming soon -- integrating the first women into the U.S. submarine force. Top Navy officials began pushing to end the men-only policy last fall and are expected as soon as this week to lay out a plan for ushering female sailors aboard.

"Once you lock these sailors into a submarine, the stress level is incredible," said Master Chief Petty Officer Randy Huckaba, the top enlisted sailor for one of the Florida's two crews, who estimates a third of the 160-man crew smokes. "There are times when the only release is to smoke a cigarette or go listen to music."

For years the Navy assumed that, aside from smoke wafting around a sub's designated smoke pit, secondhand smoke was scrubbed from the air by the same filters that remove fumes from cooking and cleaning chemicals.

However, a 2009 Navy study showed otherwise. The Navy tested 197 nonsmoking submarine sailors for nicotine in their systems, once while they were on shore duty and again after they returned from deployment at sea. Most had none while assigned to shore, but all tested positive for nicotine exposure after returning from patrols.

The Navy concluded all submarine sailors must be inhaling secondhand smoke, whether they could smell it or not.