Suetonius, The Deified Claudius 17
Back in the days before Britannia ruled the waves…
expeditionem unam omnino suscepit, eamque modicum. cum, decretis sibi a senatu ornamentis triumphalibus, leviorem maiestati principali titulum arbitraretur velletque iusti triumphi decus, unde adquireret Britanniam potissimum elegit, neve temptatam ulli post Divum Iulium et tunc tumultuantem ob non redditos transfugas.
Claudius undertook only a single military expedition, and a modest one at that. When he was granted triumphal ornaments by the senate he considered this too insignificant an honour for the dignity of an emperor and he wanted the glory of a proper triumph. He chose Britain as the most likely source of a triumph, as no one had made the attempt on it since the deified Julius Caesar, and at that time it was in a state of tumult because some deserters had not been given back.