Reuters

U.S. Defense Secretary Robert Gates sent a letter to lawmakers notifying them of the decision by the Navy, which could see the first women on nuclear submarines next year.

"This is fundamentally a Navy initiative, which they recently briefed to the secretary of defense. (Gates) supports it and he notified Congress of the Navy's plans," Pentagon press secretary Geoff Morrell said.

Women account for about 15 percent of the more than 336,000 members of the U.S. Navy and can serve on its surface ships. But critics have argued that submarines are different, pointing to cramped quarters where some crews share beds in shifts -- a practice known as "hot bunking."

A likely scenario would see female officers becoming the first to join crews on the Navy's fleet of 71 submarines, since officers have separate accommodations, a U.S. defense official said.

Congress has 30 days to provide its official comment on the Navy's decision.

Nancy Duff Campbell, an advocate for expanding the role of women in the U.S. armed forces, applauded the decision and said she did not expect any opposition from lawmakers.

"This is something that has a lot of support (within the military) and the Navy has a serious plan" to carefully integrate submarine personnel, she said.

Allowing women on submarines would be another step forward in expanding the role of women in the U.S. military. In 2008, a woman was promoted to the rank of four-star general for the first time.

Testifying in the Senate on Tuesday, Army General George Casey said he thought it was time to re-examine the policy that places restrictions on women in combat roles.

"We don't have an active effort going on, but I think it's time," Casey said.

Women are still barred from traditional frontline combat roles in the U.S. armed forces. But female soldiers often run the same risks as men in Iraq and Afghanistan, where bombings and other insurgent attacks can happen almost anywhere.

(Reporting by Phil Stewart and Susan Cornwell)