The United States Navy has decided to allow women to serve on submarines, ending one of the last all-male bastions in the US military.

Defence Secretary Robert Gates has approved the recommendation and sent letters to Congress. The move comes as the US Army's chief of staff called for a review of rules barring women from combat roles.

American women can already serve on the Navy's fleet of warships and fly fighter aircraft, but nuclear-powered subs have remained off-limits.

US naval officers previously cited the extremely tight quarters on board submarines as the main reason for barring women from them. Those in favour of lifting the ban say subs could be fitted with separate berths and bathrooms.

The decision calls for a phased approach allowing female officers to serve on submarines first. The initial group of female officers selected for the duty would first have to attend special training for submarines and for nuclear-powered vessels lasting more than 18 months.