As I mentioned in another question post, I'm greatly enjoying my non-historian jaunt through Shelby Foote.
Reading about the Seven Days Battles, we understand that the engineer McClellan sometimes took fantastic positions atop highly defensible hills, and he was able to repulse Confederate attacks, giving tremendous casualties while taking very few. Neglecting the fact that McClellan would sometimes give these positions up for ill-advised reasons, the rebels would sometimes make repeated disastrous attacks against them before they fell. My question is, if daylight attacks through the open field were near suicidal, why didn't the Confederates cross the open fields in front of the hill at night and wait in position for an early morning attack at point blank range?
My understanding is that the ubiquity of rifles, a result of the Minie Ball rendering muskets obsolete, made massed formation attacks very deadly compared to battles just a few years or decades earlier. Whereas in the age of musketry, a mass formation would sustain only one or two volleys on its way toward its objective, in the age of rifles several volleys could be put on target in the same amount of time, making exactly these types of open field advances much more deadly. So then, even when not advancing on a hill, but anytime you expect to advance to a prepared position, it seems obvious to me that you should attempt to do so under cover of night and be right up in front of your target before sunrise.
I understand that you run into the danger of veering off and missing your target, of mixing regiments up in the night, and of running into enemy pickets (or even going too far and running into your target before sunrise), but these seem like small prices to pay, especially if attacks had been repulsed repeatedly throughout the day.
I understand that commanders would often march their men towards their targets during the night to achieve surprise, but never the point of contact. This makes sense to me, as when entering a new AO commanders would want to get a view of the field before committing their troops, but in the case of a field that they've been fighting on all day, it seems like an obvious solution to cross open terrain at night. What am I missing here?
There are several things at play here I think we can note. And just sticking to the 7 Days since it was the example you mention triggering the question.
Being just how damn hard it was to coordinate the actions of any sizeable force for either army in the summer of 1862. For most units on either side the Peninsula was their first taste of real fighting and many were still learning their trade. And that meant commanders still had to figure some shit out as it were. And some also just werent up to vigorous leadership. And once you pile on casualties, it became a hard enough task just to keep a single unit coherent and in contact with its next tier. To take an example of a unit that fought and was roughly handled several times in the 7 Days, the Pennsylvania Reserves division in V Corps had their Division commander and a Brigadier captured, another wounded, and a replacement brigade commander killed! While McClellan also took the position of being remarkably passive, and only feeling he could trust a few of his corps commanders.
Lee also would have trouble with finding subordinates he could rely on at all levels, some didnt measure up, some were undone by circumstances like Magruder, and some performed uncharacteristically poorly like Jackson.
You can only fight at night if you can pin the enemy in place. Once the Army of the Potomac's right wing was back south of the Chickahominy and really even before McClellan was firmly fixed of pulling back. As the various corps pulled back through Savage's Station and through the White Oak Swamp they often marched for most of the night with a few in the rear then either being forced to stop to fight in the day, or as at Savage's Station, being forced to fight because the enemy was there and they had no real orders from above leaving most of 3 different corps on their own without unified command because Sumner wasnt trusted by McClellan as the senior on the spot. But nobody was inclined to remain where they were very long, leading to Heintzelman to risk the entire group by pulling his units out without telling the others. But everyone wanted to get under the Navy's guns ASAP. Or at least almost everyone, some like Hooker and Kearny were strong advocates for a counter-attack at every opportunity.
This almost independently by Corps retreat also meant many of the same units were forced to fight and used hardest by both armies, leaving them exhausted and often in desperate need of refit or even just a few hours for officers to reorganize. The Union II, V, VI, and to a degree VI Corps all were asked to fight multiple times, often on consecutive days. While other units like Keyes' IV Corps were barely used in the fighting. Lee faced a similar issue, as Jackson's wing was late on several days it mean his center forces under Longstreet, AP and DH Hill were used up repeatedly. Its hard to plan a night attack with worn out men, or ones who cant get into position even in the day.
Pre radio night fighting is a great way to get your own men killed. Even if you generally know where the enemy is, its much harder to get several thousand men in position to do something about that without light. And doubly harder if the enemy isnt where you expect. And triply harder without experience or with exhausted troops, look at Jackson's fate to see what good trying to blunder around in the dark good do.
You seem to overestimate the nature of the ground. While the operational area did feature several open expanses, and heights and plains. It also was still well wooded, and featured smaller farms separated by woodlands. Along with White Oak Swamp, and the Chickahominy with its swampy wooded banks. All terrain that caused entire wings of Lee's Army, who nominally should have an easier time, to get lost and turned around for hours on. Asking to fight over the same ground in darkness wasnt going to let them find their way easier.
The enemy gets a say too, while it was bottle-necked, the AotP was in a posture of only temporarily paused retreat for the 7 Days almost from the start. While Lee's senior commanders were often hours late effecting his orders, while adding in the element of trying to use cover of darkness would only give the AotP further time to escape the trap Lee was trying to catch them in. Even other solid defensive positions like V Corps and reinforcements on the North Bank of the Chickahominy had been abandoned when pressed, so it is fair to say the ANV had seen strong positions abandoned after a good punch.