That's not unknown in the history of the service, either.

Up until that point, she was virtually unknown in her own country.

At this time she was almost unknown in the West.

He was almost unknown in the West until the early 1980s.

This is a state of affairs unknown in human history.

Perhaps they are unknown in your part of the world.

From the known to the unknown in a split second.

It was rare but not unknown in women her age.

However, she was unknown in the rest of the world.

And this practice is not unknown in other media, either.