Category Research & Analysis

Hadn’t done a blog post in the while. Been focused on getting a book done. Sorry.

There is a rule of thumb often quoted out there and often put in war games that a unit becomes ineffective or reaches a breakpoint at 40% casualties. The basis for this rule is a very limited body of studies and analysis.

First, I have never seen a study on when a unit become ineffective. Even though it is now an accepted discussion point, I have not seen such a study establishing this relationship and do not think that such a study exists. I am not saying that there is not a relationship between casualties and unit effectiveness, what I am saying that I have never seen a study establishing that 1) this relationship exists, and 2) what are its measurements, and 3) what is the degree of degradation.

What has been done is studies on breakpoints, and over time, a rule of thumb that at 40% a unit “breaks” appears to be widely accepted. It appears that this rule has then been transferred to measuring unit effectiveness.

The starting point for “breakpoints” study is Dorothy Clark’s study of 43 battalions from World War II done in 1954. That study showed that the average casualties for these battalions was around 40%, although the ranged from around 1% to near 100%. Her conclusion was that “The statement that a unit can be considered no longer combat effective when it has suffered a specific casualty percentage is a gross oversimplification not supported by combat data.” She also stated “Because of wide variations in data, average loss percentages alone have limited meaning.”. We have discussed this before, see: C-WAM 4 (Breakpoints) | Mystics & Statistics (dupuyinstitute.org) and April | 2018 | Mystics & Statistics (dupuyinstitute.org) and Breakpoints in U.S. Army Doctrine | Mystics & Statistics (dupuyinstitute.org) and Response 3 (Breakpoints) | Mystics & Statistics (dupuyinstitute.org). 

The next point is the U.S. Army’s Maneuver Control manuals (FM 105-5) which in 1964 set the attacker’s breakpoint at around 20 percent casualties and the defender’s breakpoint at around 40 percent at the battalion-level. Charts in the 1964 Maneuver Control field manual showed a curve with the probability of unit break based on percentage of combat casualties. Once a defending unit reached around 40 percent casualties, the chance of breaking approached 100 percent. Once an attacking unit reached around 20 percent casualties, the chance of its halting (type I break) approached 100 percent, and the chance of its breaking (type II break) reached 40 percent. These data were for battalion-level combat. 

We have never found any studies establishing the data for these Maneuver Control manuals and we do not think they exist. Something may have been assembled when they were writing these manuals, but we have not been able to find any such files. Most likely, the tables were extension of the Dorothy Clark study, even though she said that it should not apply.

Anyhow, that is kind of it. Other stuff had been published on breakpoints, Helmbold in 1972, McQuie in 1987 (see: Battle Outcomes: Casualty Rates As a Measure of Defeat | Mystics & Statistics (dupuyinstitute.org)) and Dupuy in the late 1980s, but I have not seen anything of significance since, as it appears that most significant studies and analysis work stopped around 1989. 

Now, Dr. Richard Harrison, who spends a lot of time translating old Soviet documents, has just sent me this: 

“Supposing that for the entire month not a single unit will receive reinforcements, then we will have a weakening of 30%, with 70% of the troops present. This is a significant weakening, but it does not yet deprive the unit of its combat strength; the latter’s fall begins approximately with losses of 40%.”

His source is: 

N.N. Movchin, Posledovatel’nye Operatsii po Opytu Marny i Visly (Consecutive Operations on the Experience of the Marne and Vistula) (Moscow and Leningrad: Gosudarstvennoe Izdatel’stvo, 1928), page 99.

So, the U.S. came up with the 40% rule in 1954 which it disowned and then adopted in 1964 regardless. And here we have a 1928 Russian writing which is directly applying a 40% rule to unit effectiveness. I have no idea what the analytical basis is for that statement, but it does get my attention.