The San Diego-based amphibious ship, the Dubuque, is not being allowed to leave San Diego because of an apparent outbreak of swine flu.

There is one confirmed case on the ship and up to 50 suspected or probable.

All 420 crew members are taking Tamiflu, either as a treatment or a prophylaxis.

This is the first time military operations have been affected by the virus.

The Dubuque was scheduled to deploy on June 1 to take part in an exercise delivering humanitarian supplies to the South Sea Islands.