Carroll's involvement in the Civil War began in earnest in 1861 when she embarked on a mission to advise Union generals and policymakers on military strategy and political matters. Despite facing skepticism and resistance due to her gender, Carroll's persuasive arguments and strategic insights soon won over key figures in the Union government. Carroll is recognized by modern historians as "the great unrecognised member of Lincoln's cabinet"

One of Carroll's most significant contributions to the Union cause was her advocacy for the strategic importance of the Western theater of the war. Recognizing the economic and logistical advantages of controlling the Mississippi River, Carroll embarked on a journey with Army Officer Lemuel Evans where she proposed strategic plans to Union leaders. Carroll advocated for the utilization of the Tennessee River as a route for Union gunboats, a plan that proved successful with the capture of Forts Henry and Donelson. 

In addition to her strategic counsel, Carroll also played a crucial role in shaping Union policy regarding emancipation and the recruitment of African American soldiers. She argued passionately for the enlistment of Black troops and the implementation of emancipation as a military strategy to undermine the Confederacy's economic and social infrastructure.

Anna Ella Carroll requested compensation of $5,000 for her involvement in the war and in particular the Tennessee Plan.  Her requests for compensation were largely denied or ignored by the U.S. government. You can read the entirety of her request at the Library of Congress.  Lincoln responded by saying that this was the "most outrageous one [demand], ever made to any government, upon earth!

Despite her significant contributions, Carroll's role in shaping Union strategy during the Civil War has often been overlooked or downplayed in historical accounts. However, recent scholarship has begun to recognize and celebrate her achievements, shedding new light on her legacy as a pioneering woman in American military and political history.

Anna Ella Carroll's military genius is evidenced by her:

• Strategic Insight: Carroll demonstrated an exceptional understanding of military strategy and warfare dynamics. Her proposals and recommendations regarding military campaigns, troop movements, and strategic objectives showcased her ability to grasp the complexities of military operations.
• Western Theater Strategy: Carroll's advocacy for prioritizing the Western theater of the war, particularly the importance of controlling the Mississippi River, proved to be strategically prescient. She argued that gaining control of key points along the Mississippi would sever Confederate supply lines and divide the South, weakening its ability to sustain the war effort.
• Campaign Success: The implementation of Carroll's strategic recommendations led to several successful Union campaigns and victories in the Western theater, including the capture of key Confederate strongholds such as Forts Henry and Donelson, Vicksburg, and New Orleans. These victories significantly weakened the Confederacy and contributed to the Union's ultimate triumph in the war.
• Emancipation and African American Soldiers: Carroll's advocacy for the enlistment of African American soldiers and the implementation of emancipation as a military strategy demonstrated her foresight and understanding of the war's broader implications. By recognizing the potential of African American troops and the strategic advantage of undermining the Confederacy's economic and social infrastructure through emancipation, Carroll contributed to reshaping Union policy and military tactics.
• Recognition by Union Leaders: Carroll's strategic counsel was valued and respected by key Union leaders, including President Abraham Lincoln and General Ulysses S. Grant. Both Lincoln and Grant acknowledged Carroll's contributions and sought her advice on military matters, reflecting the esteem in which she was held by prominent figures in the Union government and military.