The rear three cars of the train were severely damaged.
Literal
Train [of-の] rear 3-cars [topic-は] severe damage [object-を] received.
後部３両 ('rear three cars') is a compound noun phrase: 後部 ('rear section') modifies the counter phrase 3両. 損傷を受ける ('to receive damage / to be damaged') is the formal news-style collocation. ひどい ('severe, terrible') is the everyday い-adjective for severity.