General Halleck's first assignment was to meet with General McClellan at Harrison's Landing. Each of them had different views on the best way to end the Confederate rebellion. McClellan wanted to cut Richmond's lines of communications by sending troops south of Richmond to do this. Halleck had no intentions of allowing that. Halleck's plan was to have McClellan join forces with General Pope and with this large pair of armies attack Richmond. Also, to protect the endless fear of a Confederate assault on Washington DC, Halleck wanted to keep a sizable force between Washington DC and Richmond. Halleck was willing to compromise. If his plans would not work for McClellan, then he was free to again attempt to capture Richmond with his own army plus some additional 20,000 troops on their way to help McClellan. McClellan, always fearing larger Confederate armies then what existed, asked for 30,000 troops. This left McClellan with two choices. Resume his attempt to capture Richmond or retreat from the Peninsula. McClellan's idea was not to retreat but carry on an attempt to capture Richmond.
With the defeat of McClellan in the Peninsula campaign, he had retreated to Harrison's Landing to regroup and of course fortify the Landing. In the meantime, Lincoln had summoned General Halleck to meet with McClellan there at Harrison's Landing and asses the situation. General Ambrose Burnside accompanied Halleck so as to have another top general there to discuss the military situation.
On July 25, 1862, General in Chief Henry W. Halleck, accompanied by Major General Ambrose Burnside visited Harrison's Landing to confer with General McClellan. Halleck's purpose is to pressure McClellan to do "something". Halleck orders McClellan to advance against Richmond or withdraw from the Peninsula and send troops to join Major General Pope's Army of Virginia. McClellan commits to nothing. He is placing himself and General Pope's mission in jeopardy.
The first task assigned to the new Union general in chief, Henry W. Halleck was to visit General George B. McClellan at Harrison's Landing and urge him to reinvest his army in another attempt to either capture Richmond, or place it under siege. President Lincoln gave Halleck the authority to relieve McClellan of his dutirs as commander of the Army of the Potomac if he chose to do so.
On July 25, 1862, General in Chief Henry W. Halleck visits the headquarters of General McClellan at his Virginia headquarters in Virginia. He brings General Ambrose Burnside with him. Burnside and McClellan are friends. Halleck gives McClellan a choice, and both of them will be a serious problem for McClellan. McClellan must either restart his Peninsula campaign or make a total withdrawal from Harrison's Landing. These troops will be given to John Pope's new Army of Virginia. McClellan's anger with the Lincoln government intensifies. Reportedly he has been receiving letters from his supporters in the North to march on Washington DC and take control of the government. One thing is certain, Burnside reports that anti-government agitation among McClellan's officers seem treasonous to him. The Army of the Potomac is piece by piece brought back to Washington DC to help form General Pope's new army.
With the disaster of the Peninsula campaign still remaining a lingering problem, Lincoln summons General Henry Halleck to Washington DC. On July 23, 1862, Halleck assumes the position of general in chief. He is sent to meet McClellan ans asses the situation at Harrison's Landing.
The Battle of Gaines's Mill had been a Union victory. The entrenched Union forces foiled all of General Lee's attempts to break through the Union's lines and attempt to destroy the Army of the Potomac. McClellan chose to retreat but not after Union generals Joseph Hooker and Philip Kearny pleaded their case for a counterattack to McClellan. McClellan saw only danger by remaining on the field of battle and he pursued his retreat to Harrison's Landing.
After speaking with General George B. McClellan at Harrison's Landing, he realized there was a serious weakness in the Union's situation. He reasoned that unless the Confederates perceived that McClellan threatened Richmond with a siege, they would have the liberty to exploit their interior lines to attack either McClellan on the Peninsula or Pope near Washington DC. He therefore ordered McClellan to evacuate the Peninsula and bring his army north to support Pope.
The creation of the new Union army, the Army of Virginia under the command of General Pope caused several problems for the Union. This was in the field and Washington DC problems. President Lincoln and Secretary of War Edwin Stanton saw General Pope as a possible replacement of the problematic General George McClellan. More so when Pope's political views matched those of Lincoln and the Radical Republicans. During this period, General McClellan was still at Harrison's Landing, and was more than annoyed at the appearance of General Pope. General in Chief, Henry W. Halleck had a vested interest in John Pope as he had recommended him for his new position. If Pope failed, Halleck could replace him with McClellan. If both failed, Halleck could remain as general in chief and take charge of Eastern armies. Halleck was also undermining McClellan by piecemeal reductions of his Army of the Potomac. Halleck believed that no matter what happened on the battlefield, his position had leverage and allowed him to make the important decisions.
Although General Halleck was not perfect, he did become the Union's general in chief in the Summer of 1862. With that said, Halleck deserved the opportunity President Lincoln offered to him. Halleck was a great strategist and realized that General Grant was a logical target for a Confederate assault at Pittsburg Landing, leading to the Battle of Shiloh. Halleck ordered General Buell to make a hasty trip down river to reinforce Grant. Halleck believed that unless these two armies were united, they might be outnumbered. Grant failed to follow one crucial order from Halleck, Halleck had ordered Grant to take a strong defensive position at Pittsburg Landing and to entrench his army. This General Grant failed to do.
Lincoln's Cabinet wanted him to get rid of General George B. McClellan. Or, perhaps better said, not let him be in charge of major armies, and certainly never again as general- in -chief. General Henry Halleck was in charge of the West and US Grant reported to him. Halleck believed that Grant almost failed at Shiloh. This was due to Grant being the victim of a surprise Confederate army assault and perhaps not properly fortifying his position at Pittsburg Landing. Rumors about Grant's drinking problem was also well known Lincoln urged Halleck to stay with Grant because he believed Grant was a fighting general.
On July 8, 1862, President Lincoln arrived at Harrison's Landing to meet with Major General George B. McClellan. Lincoln's purpose was to urge McClellan to renew the offensive against Richmond. However McClellan wanted to do that would be satisfactory, however, Lincoln wanted a firm commitment from McClellan, which was not forthcoming.
General Halleck was General US Grants superior officer at the time of the Battle of Shiloh. Grant's failure to entrench his army upon landing at Pittsburg Landing was a major error that could have caused a Federal defeat. Halleck was infuriated and took control of Grant's army and led it to Corinth, Mississippi.