On July 9 and July 16 of 1861, Greenhow passed secret messages to Confederate General P. G. T. Beauregard containing critical information regarding Union military movements for what would be the First Battle of Bull Run, including the plans of General Irvin McDowell. Assisting in her conspiracy were pro-Confederate members of Congress, Union officers, courier Betty Duvall, and her dentist, Aaron Van Camp, as well as his son who was also a Confederate soldier, Eugene B. Van Camp. Confederate President Jefferson Davis credited Greenhow's information with the Confederates securing victory at Manassas over the Union Army on July 21.