So if i understand well. Enter an smz is possible only with a patrol mouvement from the Oparea attach to it.
You can enter also with transit movement, but only to pass through, not end movement there (for example for passing through the Channel, or Gibraltar, etc.)
And remember 15.22: "If the submarine is moving from an OpArea to an adjacent Base (such as from the North Sea to Germany), no Transit Event roll is made UNLESS the submarine must traverse a transit zone (such
as the Bay of Biscay)."