2. McClellan not blowing through the thin defenses of Yorktown line with forces at hand.

Since no date has been forthcoming, I'll just have a look at the issue of the "thin defences".

The first thing we need to realize is that Magruder's comments about his weakness are in many cases either mistaken or lying. He claims to have to defend a line over ten miles wide, but the Yorktown line is simply not that wide:

The scale in the bottom left shows that the actual line is only a few miles long, and even that sort of overstates things because there are only a few crossing points of the Warwick. (The rest of it is deep enough that it cannot be forded.)

The crossing points, and the routes by which McClellan's force approached the Warwick line on the 5th, are shown below.

(note that the crossing point around Garrow has no road leading to it, and the same is true of Wynns Mill - neither of these is a road way to cross the Warwick and it requires recon to find them, which leads to a delay.)

On the 5th, McClellan ordered both his approaching columns to attack by bayonet charges if necessary - the left at Lees Mill and the right at the gap between Yorktown and the Warwick (the Red and White redoubts). However, neither column was able to successfully attack because of the volume of enemy firepower.

On the 6th, McClellan did not re-order an attack. On the 7th it began raining hard enough to shut down all movement for a few days.

So how many troops were there in the Warwick line on the 5th and the 6th?

The best estimate we can obtain is by looking at the actual per-regiment reported strengths from late April and cross-referencing this with regimental arrival dates.

The troops who were at Yorktown on or before the 5th of April were:

Brigade Regiment Strength Type

1: McLaws 5th LA 744 Inf

2: McLaws 10th LA 595 Inf

3: McLaws 15th VA 476 Inf

4: McLaws Noland Battalion 162 Inf

5: McLaws Garrett 50 Art

6: McLaws Young 57 Art

7: Cobb 16th GA 488 Inf

8: Cobb 24th GA 660 Inf

9: Cobb 2nd LA 782 Inf

10: Reserve 10th GA 582 Inf

11: Ewell 32nd VA (1 coy) 29 Inf

12: Ewell 52nd Va Mil 30 Inf

13: Ewell 68th Va Mil 20 Inf

14: Ewell 115th Va Mil 40 Inf

15: Ewell Old Dom Rifles 60 Inf

16: Ewell Allen's battalion 500 Art

17: Ewell Companies Art 121 Art

18: Colston 3rd VA 550 Inf

19: Colston 13th NC 575 Inf

20: Colston 14th NC 625 Inf

21: Wilcox 9th AL 550 Inf

22: Wilcox 10th AL 550 Inf

23: Wilcox 11th AL 656 Inf

24: Wilcox 19th MS 800 Inf

25: Wilcox Stanard 60 Art

26: Winston 8th AL 800 Inf

27: Winston 14th AL 700 Inf

28: Winston 14th LA 750 Inf

29: Winston Macon 60 Art

30: Ward 2nd FL 530 Inf

31: Ward 2nd MS Battalion 360 Inf

32: Rains 13th AL 474 Inf

33: Rains 26th AL 283 Inf

34: Rains 6th GA 703 Inf

35: Rains 23rd GA 370 Inf

36: Rains 19 batteries, Yorktown 1151 Art

37: Crump 46th VA 356 Inf

38: Crump 9th VA Mill 29 Inf

39: Crump 21st VA Mill 39 Inf

40: Crump 61st Va Mill 201 Inf

41: Crump Det Cav 18 Cav

42: Crump Det East Shore 58 Inf

43: Crump Matthews Lt Dr 40 Cav

44: Crump Armistead 46 Art

45: Crump Heavy Art 332 Art

46: Reserve Arty Pendleton 720 Art

47: Magruder Magruder's cav 990 Cav

48: Wise Wise and Hampton cavalry 700 Cav

Which totals

Type Strength

1: Inf 14627

2: Art 3097

3: Cav 1748

That's what's there the day McClellan reaches Yorktown.

As for arrivals on the 6th:

Brigade Regiment Strength Type Arrival

1: Cobb Cobb's 594 Legion April 6

2: Early 20th GA 560 Inf April 6

3: Early 23rd NC 540 Inf April 6

4: Early 24th VA 740 Inf April 6

5: Early Jeff Davis 80 Art April 6

6: Rodes 5th AL 660 Inf April 6

7: Rodes 6th AL 1100 Inf April 6

8: Rodes 12th AL 550 Inf April 6

9: Rodes 12th MS 650 Inf April 6

10: Rodes King William 80 Art April 6

Type Strength

1: Legion 594

2: Inf 4800

3: Art 160

Their dispositions on the 6th are:

I do not see a way to simply roll over Magruder's force. He has ~2,000 infantry to oppose each of the crossing points (with 5,000 in the rear as reserves if need be) and another 6,500 covering the mile or so from the head of the Warwick flooded region to the York river, plus over 3,200 gunners (which is to say, on the order of 160 guns). As a point of trivia interest it is almost as strongly defended as Vicksburg in terms of total men*, and notably more concentrated per mile.**

*After the casualties in the field battles Vicksburg's defenders were not more than 25,000 men all told, and counting troops that arrived on the 6th the defenders of the Warwick line were also 25,000 men all told. It is unclear if the categories were the same, but if they differed it is in favour of the Warwick forces being larger.

** The Vicksburg defences are about 6.5 to 8 miles of perimeter that all needs to be defended, while the Warwick line can be concentrated on a few points of attack and is only about five miles long counting the whole length.

There were missed opportunities at the Warwick line, but "just roll straight over them" is not one of them.