U.S., Britain Plan Seaborne Attack on Iraq-Source By Peter Graff LONDON (Reuters) - The United States and Britain are planning a massive seaborne invasion of Iraq from the Gulf as the first stage in any ground war, a British defense ministry source said on Saturday. "Discussions on future amphibious operations are at an advanced stage," the source said, adding that Britain would commit its elite 3 Commando Brigade of Royal Marines to the proposed invasion. In the 1991 Gulf War U.S.-led forces assembled a large amphibious task force in the Gulf, but never mounted an assault by sea. Instead, infantry...