Quartermaster's Mate Leslie Harmon, [Reed Diamond], is awaiting a court martial when he is brought before Commodore Joseph Smith [E.G. Marshall] and his son Lieutenant Joseph B. Smith Jr. [Kevin O'Rourke]. Harmon has deliberately interfered with the militarily necessary demolition of the dry dock at Hampton Roads Naval Base in an effort to prevent collateral damage and civilian casualties as Confederate forces overran the base. This tense setup launches a tale of loyalties, espionage, and naval courage set against a pivotal moment in the Civil War.
Harmon is introduced to Miss Betty Stuart, [Virginia Madsen], a Virginia Southern belle educated in Baltimore who hopes to help Harmon spy on the Confederate States Navy at Gosport on the raised and refitted USS Merrimack, now the ironclad CSS Virginia. Once in the South, Harmon encounters many key naval officers and learns that the armor test on 3 inches (76 mm) of iron plate is staged to mislead any Union spies—like him. In reality, Virginia boasts 4 inches (100 mm) of armor and cannot be pierced by any Union guns. Harmon and Betty realize that this information must reach Washington to improve firepower to sink Virginia. This revelation sets the stage for a dangerous game of deception and counterintelligence that could alter the balance of naval power.
Betty experiences a turning point when she discovers that her childhood friend and lover, Lieutenant Catesby ap Roger Jones, [Alex Hyde-White], has been reassigned as the second-in-command of Virginia and is now in danger because of the very intelligence she intended to transmit north. She attempts to halt Harmon from carrying the intelligence back, but he proceeds anyway. At the commissioning ceremony for Virginia, she confesses to her now-fiancé that she had helped Harmon infiltrate the shipyard and spy for the Union, warning him of the possible increase in firepower. He is stunned and distraught by her betrayal, yet sails to war without turning her in, choosing to preserve their fragile bond as a final act of love for his traitorous fiancée. Virginia sails off to break the Union blockade at Hampton Roads. Betty is promptly arrested by Lt. Guilford [Philip Casnoff], an admiral’s aide and spy hunter, on suspicion of espionage.
Virginia first approaches USS Congress as her skipper, Lt. Smith, rallies his men on board to do their duty. Captain Franklin Buchanan [Leon B. Stevens] of Virginia rallies his men similarly. Congress fires a full broadside into Virginia to no effect. In the ensuing action, Virginia bypasses Congress, promptly sinks USS Cumberland, and returns to sink Congress. Lt. Smith is killed; taking over command, executive officer Lt. Pendergrast orders the ship’s surrender. Though Virginia’s crew are jubilant, rifle fire from Union troops ashore enrages Captain Buchanan. He goes topside to return fire and is wounded, thereupon ordering Jones to assume command and set Congress ablaze.
That same night, Lt. Guilford interrogates Betty, who denies being a spy based on an intercepted letter to her from Lt. Smith. She is informed then of Smith’s death aboard Congress. When told that her fate would be the gallows if she does not cooperate, she hopes for the courtesy shown an executed spy the day before (whose hanging she witnessed). Lt. Guilford rebuffs her, displaying his contempt for her treason when compared to the bravery of the hanged soldier who fought for his side.
During the night, USS Monitor sails between the burning Congress and Virginia to protect USS Minnesota, which has run aground and is defenseless until high tide returns the next day. Only the low tide has prevented Virginia from finishing off Minnesota. Captain Worden delivers orders to Monitor, while Harmon volunteers his service as a pilot. Worden makes Harmon, familiar with Hampton Roads and Virginia, a midshipman on the spot.
The morning of the second day of battle, Jones sights Monitor and describes her as > "the test we face." Worden does his best to engage Virginia as far from Minnesota as he can, aided by Monitor’s shallower draft, greater maneuverability, and the damage sustained by Virginia the previous day. As the two ships exchange fire, Virginia runs aground, but is able to pull free. Jones attempts to ram the Monitor but fails to do significant damage; Worden orders a return ram, but is blinded when a shell from Virginia strikes Monitor’s pilot house. Monitor withdraws, having delayed Virginia from sinking Minnesota. In view of the damage to Virginia, the exhaustion of his crew, and the falling tide, Jones also decides to retire back to port.
Both sides claim victory, although the Monitor saved the rest of the blockade from destruction. Her designer, John Ericsson [Fritz Weaver], has an argument with Secretary of the Navy Gideon Welles over the use of insufficient powder in Monitor’s guns to sink Virginia: Welles’s officers respond that it was a calculated decision to prevent the guns from exploding and protect the lives of the crew.
Back at Gosport, Lt. Guilford is pleased to release Betty, informing her that she saved Virginia based on a report by Lt. Jones. Demonstrating Southern chivalry, he is relieved not to have to hang her. In truth, Lt. Jones used Betty’s confession the day before to send false intelligence to the Union, which resulted in the lesser powder charges used by Monitor. Lt. Jones tells Betty that he could not bear to see her hang, but that he can never be with her again due to her treason. She is sent north, forever marked as a traitor to her family, friends, and fellow Virginians.
A voice-over narration notes that Virginia was scuttled two months later after Union troops took Norfolk, and that Monitor sank off Cape Hatteras at the end of the year.
