When the Romans returned in 43 AD they had controlled the Atlantic Seaboard for ninety years, so Claudius was more properly prepared for a long campaign; not just an army, but a navy also, since control of the sea was key to taking and holding an Island.
When Agricola made the first significant push into the north in the early 80s he had a naval presence on both coasts and even thought about an expedition to Ireland. Then, after the near disaster of the Boudicca revolt, the south was secured, and Rome was on the offensive, initially in the west and then in the North. In a typically aggressive series of campaigns Agricola punched his way north culminating in a battle of Mons Graupius, where his auxiliary troops reportedly killed about a third of a thirty thousand man highlander force.