Berthierville II: Attack of the Corps (the ORBAT)

Berthierville II: Attack of the Corps 

In a previous post we looked at the Battle of Berthierville, and the clumsy comparison to the Alma along with the parallels to Stones River.
If one actually looks closer at the order of battle, however, the situation becomes even odder.





US Strength
The US force here consists of what were historically 15^th and 20^th Corps (here 15^th and 12^th) plus a cavalry division. The strength of 15^th Corps and the Cavalry is mentioned as being 30,000 troops.
However, counting strengths is never very easy.
In past correspondence, TFSmith has indicated that for “strength” (for US troops) he uses Aggregate Present and Absent – this meaning the total number of men on the rolls, including those currently absent with or without leave. (Present for Duty includes those on extra duty, under arrest and sick; since extra duty includes logistical matters and supernumaries such as cooks, it is an overestimate of the line strength.)
The 12^th Corps (OTL 20^th) was formed by the 2^nd Division under McCook – veterans of Shiloh, but that did not actually takes place in this timeline – with the addition of 9^th under Mitchell and the 11^th under Sheridan. Both of these divisions were formed in Sept-Oct 1862 OTL, and would be very new troops.
Of these, the 2^nd was “filled up” and was 11,000 present-and-absent or 8,000 present-for-duty (meaning maybe 6,000 actual line shooters); the two new divisions were about 20,000 P&A or 14,500 PFD (11,500 or so in the line).
Total fighting strength of 12^th Corps is about 17,000 to 18,000 troops.



The 15^th Corps has Prentiss' division added (historically captured at Shiloh) and OTL the two non-captured divisions were over 20,000 Aggregate Present and Absent – but only about 13,000 PFD (10,000 or so in the line). This means that, with Prentiss, a rough approximation is 15,000 to 17,000 troops in the line of battle.



Michigan State Troops are also present, but in reality in 1862 the Michigan militia in 1862 consisted of a few companies each Active State Guard and home guard. This can essentially be ignored.



The total estimate of Union troops in the line of battle is about 32,000 infantry – roughly, each division is 5,000 to 6,000 troops, and two of them are very new indeed.






British strength
The British have two brigades of cavalry (which amounts to roughly 3,000 effectives) and four three-brigade divisions. Each British brigade is somewhere between 2,000 and 2,500 effective infantry, with the logistics handled by the Military Train and Royal Engineers, no need to detach troops to man the batteries (that's the Royal Artillery) and with militia to act as bridge guards or other minor details. In short, the British have roughly 27,000 infantry and 3,000 cavalry – so they are not outnumbered at all, in fact the two armies are essentially identical in size. (If all battalions were at establishment strength of 40 officers and 850 Other Ranks, this would be roughly 32,400 infantry.)



The reason for this is simple – British battalions worked on a system of maintaining effective shooters (and would send reinforcements from the depots to keep battalions up to strength) while American regiments worked on a system of muster strength (i.e. sign up 1,000 men and then never recruit up again).
The net result of all this is that the British may slightly outnumber the Americans – this is entirely due to the way that TFSmith is measuring the Americans by Aggregate Present and Absent (which they signally failed to achieve) and the British by Effectives (which they managed to keep fairly close to establishment, though he feels they would not). Combined with the way the British have the initiative (and are attacking a part of the Union army with the whole of their own) this should result in a major British numerical advantage at the point of contact.






The Royal Navy
There's no clear reason given for why there's only four gunboats, or why they're not armed with Armstrong guns. They should have a 40 pounder and a 110 pounder Armstrong at this point (or, in the case of Heron, been fitted with two 110 pounder Armstrong as built), and (if the Lakes are inaccessible) there should be about ten times as many of them.






Results of this



With this information we can try to work out correlations of space. Armed with the information that an American division of 5-6,000 shooters in line (with a small reserve) is about a mile in frontage, we can come to a series of surprising conclusions.



Reynolds is at Saint-Norbert. Prentiss is at Saint-Cuthbert, four and a half miles away – so there is a huge three-mile hole between them.
Hurlbut is at Sainte-Elizabeth, five miles from Reynolds and seven from Prentiss.
Wood is near Saint-Thomas, and has about four and a half miles between his position and that of Hurlbut.
Mitchell at Lanoraie is seven miles from Wood.
And Negley is apparently six miles further back. (This is the least clear of all.)

See the bottom of the post for a map.


This all seems to suggest a distinctly 20^th Century view of how much frontage a division can cover (on the order of a mile per 1,000 men), and as described every US formation has huge, gaping open flanks on both sides. They are so far apart that any reinforcing movement would take at least an hour's march, and the British should be able to march down the main road, block it, and then overwhelm the scattered divisions in detail. (If instead the line is supposed to be continuous, then it is a line with roughly 1,000 men per mile – too thin to provide effective resistance against cavalry, let alone infantry.)
As it happens, the “third division” attack we see (which is less successful than the one at Stones River) is about 7.5 thousand British troops hitting 5-6 thousand American troops, by surprise, in the flank. They should be routed.
The British 1^st and 2^nd Divisions (approx. 15,000 shooters) apparently frontally assault 15,000 men, but as noted above they're actually attacking only one division.







This is an excellent example of why to be careful when writing up military situations – TFSmith has accidentally created the situation for a spectacular British victory, though he did not manage to notice.




Map of apparent Union and British positions, with rough frontages (when deployed in single two-deep line) noted for those troops not making attacks. Note the scale - if the centre of Mitchell's division was on the Round Tops at Gettysburg, Wood's division would be half a mile north of the northernmost tip of the Fish Hook.)