From 1938 until 1946, it operated as a clandestine organization.

He became a member of a clandestine political organization comprising army colonels.

No, this is not a secret meeting of some clandestine organisation seeking to rule the planet.

When the government banned this group, it remained in existence as a clandestine organisation.

"You have a clandestine military organization trained by Russians?"

Montoneros became a clandestine organization once more, and outlawed by the government a year later.

There are clandestine organizations all over the state that promote this dangerous sport.

Many small, clandestine organizations were drawn to this group.

Several clandestine organizations were preparing for an uprising when Alexander died unexpectedly in 1825.

I've got a feeling that a clandestine organization of resistance is already in existence.