Final answer:
Harriet Tubman's most notable contribution to the Union was leading a raid that freed over 700 enslaved individuals. She also served in various capacities, such as a nurse and spy for the Union. Her actions and the enlistment of African-American soldiers were vital to the Union war effort and the eventual victory.
Step-by-step explanation:
Harriet Tubman's contribution to the Union war effort is most accurately described by C. Harriet Tubman led a Union raid that resulted in over 700 enslaved people being freed. During the Civil War, Tubman's roles were multifaceted, including serving as a scout, a spy, and a nurse. However, her most notable military contribution was planning and leading the Combahee River Raid in South Carolina in June 1863, which freed more than 700 enslaved people.
Aside from mobilizing African-American troops, the Emancipation Proclamation was significant in that it allowed for the formal enrollment of African-American men into the Union Army. Tubman's efforts significantly contributed to the war and bolstered the Union's manpower. Ultimately, the inclusion of African American soldiers was crucial for the Union's victory, with close to 200,000 serving by the war's end. Her work, along with the efforts of many others, helped shape the path toward emancipation and redefine the objectives of the Civil War.