Ergänzung: Zu finden ist die Regelung in den Core Rules unter Transports s. 17 ...
Unless otherwise stated, units cannot do anything or be affected in any way while they are embarked.
... bzw. in den Rules Commentary unter Embarked Units:
Embarked Units: Units embarked within a Transport do not count as being on the battlefield for any rules purposes. This means that, unless explicitly stated otherwise, embarked units cannot do anything (e.g. shoot, fight, use abilities, etc.). Similarly, you cannot select an embarked unit as a target for any rules, including Stratagems.