Such a move is rare, but not unprecedented.

这样的举动少见，但并非从来没有过。

In 1987 the Socialists took the unprecedented step of appointing a civilian to command the force.

在1987年，社会党人史无前例地任命一名非军队出身的人来领导军队。

The mission has been hailed as an unprecedented success.

这次行动被认为是一次空前的成功。

an instant slaughter unprecedented in the history of mankind.

一场人类历史上空前的即时大屠杀。