Question: Was Operation Diadem or the Battle of Cold Harbor fought during the Civil War?

Context articles: Battle of Cold Harbor
David P. Casey
Operation Diadem order of battle
Cold Harbor Union order of battle
Cold Harbor, Virginia
Battle of Gaines's Mill
Operation Diadem
Native Americans in the American Civil War
Terrence Begley
Cold Harbor Confederate order of battle

The Battle of Cold Harbor was fought from May 31 to June 12, 1864, with the most significant fighting occurring on June 3.
 It was one of the final battles of Union Lt. Gen. Ulysses S. Grant's Overland Campaign during the American Civil War, and is remembered as one of American history's bloodiest, most lopsided battles.
 Thousands of Union soldiers were killed or wounded in a hopeless frontal assault against the fortified positions of Confederate Gen. Robert E. Lee's army.
David P. Casey (1842 – January 4, 1893) was an Irish soldier who fought in the American Civil War.
 Casey received the United States' highest award for bravery during combat, the Medal of Honor, for his action during the Battle of Cold Harbor in Virginia on 3 June 1864.
 He was honored with the award on 14 September 1888.
Operation Diadem order of battle is a listing of the significant formations that were involved in the fighting on the Winter Line and at the Anzio bridgehead south of Rome during "Operation Diadem" in May - June 1944 which resulted in the Allied breakthrough at Cassino and the breakout at Anzio leading to the capture of Rome.
The following Union Army units and commanders fought in the Battle of Cold Harbor (May 31–June 12, 1864) of the American Civil War.
 The Confederate order of battle is listed separately.
 Order of battle compiled from the army organization May 31, 1864, army organization May 26-June 3, 1864, the casualty returns and the reports.
Cold Harbor is an unincorporated community in Hanover County, Virginia.
 The Battle of Cold Harbor was fought in the area in 1864, during the American Civil War.
The Battle of Gaines's Mill, sometimes known as the First Battle of Cold Harbor or the Battle of Chickahominy River, took place on June 27, 1862, in Hanover County, Virginia, as the third of the Seven Days Battles (Peninsula Campaign) of the American Civil War.
 Following the inconclusive Battle of Beaver Dam Creek (Mechanicsville) the previous day, Confederate General Robert E. Lee renewed his attacks against the right flank of the Union Army, relatively isolated on the northern side of the Chickahominy River.
 There, Brig. Gen. Fitz John Porter's V Corps had established a strong defensive line behind Boatswain's Swamp.
 Lee's force was destined to launch the largest Confederate attack of the war, about 57,000 men in six divisions.
 Porter's reinforced V Corps held fast for the afternoon as the Confederates attacked in a disjointed manner, first with the division of Maj. Gen. A.P. Hill, then Maj. Gen. Richard S. Ewell, suffering heavy casualties.
 The arrival of Maj. Gen. Stonewall Jackson's command was delayed, preventing the full concentration of Confederate force before Porter received some reinforcements from the VI Corps.
Operation Diadem, also referred to as the Fourth Battle of Monte Cassino or, in Canada, the Battle of the Liri Valley, was an offensive operation undertaken by the Allies of World War II (U.S. Fifth Army and British Eighth Army in May 1944, as part of the Italian Campaign of World War II.
 "Diadem" was supported by air attacks called Operation Strangle.
 The opposing force was the German 10th Army.
Native Americans in the American Civil War saw Native American individuals, bands, tribes, and nations participate in numerous skirmishes and battles.
 Native Americans served in both the Union and Confederate military during the American Civil War.
 They were found in the Eastern, Western, and Trans-Mississippi Theaters.
 At the outbreak of the war, for example, the majority of the Cherokees sided with the Union, but soon after allied with the Confederacy.
 Native Americans fought knowing they might jeopardize their sovereignty, unique cultures, and ancestral lands if they ended up on the losing side of the Civil War.
 28,693 Native Americans served in the Union and Confederate armies during the Civil War, participating in battles such as Pea Ridge, Second Manassas, Antietam, Spotsylvania, Cold Harbor, and in Federal assaults on Petersburg.
Sergeant Terrence Begley (died 25 August 1864) was an Irish soldier who fought in the American Civil War.
 Begley was awarded the United States' highest award for bravery during combat, the Medal of Honor, for his action during the Battle of Cold Harbor in Cold Harbor, Virginia on 3 June 1864.
 He was honored posthumously with the award on 1 December 1864.
The following Confederate States Army units and commanders fought in the Battle of Cold Harbor (May 31–June 12, 1864) of the American Civil War.
 The Union order of battle is listed separately.
 Order of battle compiled from the army organization during the battle and the reports.