Civil War Fact Check

Any civil war buffs out there heard of this one:

Equally valuable intelligence was provided to the Union navy by black Americans. Two examples of strategic importance occurred during the late 1861-early 1862 period. Mary Touvestre, a freed slave, worked in Norfolk as a housekeeper for an engineer who was involved in the refitting and transformation of the USS Merrimac into the Virginia, the first Confederate ironclad warship. Overhearing the engineer talking about the importance of his project, she recognized the danger this new type of ship represented to the Union navy blockading Norfolk. She stole a set of plans for the ship that the engineer had brought home to work on and fled North. After a dangerous trip, she arrived in Washington and arranged a meeting with officials at the Department of the Navy. 

The stolen plans and Touvestre's verbal report of the status of the ship's construction convinced the officials of the need to speed up construction of the Union's own ironclad, the Monitor. The Virginia, however, was able to destroy two Union frigates, the Congress and the Cumberland, and run another, the Minnesota, to ground before the Union ironclad's arrival. If the intelligence from Touvestre had not been obtained, the Virginia could have had several more unchallenged weeks to destroy Union ships blockading Hampton Roads and quite possibly open the port of Norfolk to urgently needed supplies from Europe.

Fascinating, if true. But I've read quite a bit about the ironclads, and never come across this tale.