Shipping sources at the Suez Canal said that a United States nuclear submarine and a supply ship of the US Enterprise aircraft carrier convoy crossed the key water strait Saturday while on their way to the Mediterranean under tight security.  Sources said that the submarine USS Toledo and the supply ship USS James E Williams crossed the Suez Canal within the southern convoy coming from the Red Sea on their way to the Mediterranean.  Sources added that the two US military forces were centered in the Gulf of Aden zone within the US Enterprise aircraft carrier battle group which was preparing to leave the area as soon as the aircraft carrier John Stennis arrived near Gulf waters. The final destination of the two breakaway forces is unknown. The security procedures during the crossing of included stopping the movement of the ferries which transported passengers and cars between the two shores of the Canal, stopping trucks and vehicles on the bridge of the Suez Canal, preventing small fishing boats from approaching the waterway and not allowing vehicles on the parallel road to Suez Canal, except the ones of the Suez Canal itself. The Suez Canal Authority announced that 40 ships crossed the Canal on Saturday in both directions.