The Defensive Value of Urban Terrain

I probably should have blogged about this long ago, but you now, it is hard to stay on top of the blog and keep working on all various books that I keep signing contracts for.

Anyhow, we started getting hits on this blog from this article:  Urban Operations in Ukraine: Size, Ratios, and the Principles of War – Modern War Institute (usma.edu)

They specifically say:

“A military axiom is that an attacking force should outnumber defenders at the tactical level of war by a ratio of 3:1 to have a reasonable chance for success. Some analysts, including those responsible for US Army doctrine, believe a ratio as high as 6:1 is sometimes necessary to achieve success in urban operations because of the increased strength of the defense on urban terrain. Regardless of the actual requirements, force ratios are relevant for urban planners.”

This link to us is in reference to the 6:1 figure, and leads to blog post: U.S. Army Force Ratios | Mystics & Statistics (dupuyinstitute.org)

Now, I do not know why they would use that link. I clearly am disputing the army doctrine figures with my charts from page 10 and 210 of War by Numbers:

European Theater of Operations (ETO) Data, 1944

Force Ratio                       Result                          Percent Failure   Number of cases

0.55 to 1.01-to-1.00            Attack Fails                          100%                     5

1.15 to 1.88-to-1.00            Attack usually succeeds        21%                   48

1.95 to 2.56-to-1.00            Attack usually succeeds        10%                   21

2.71-to-1.00 and higher      Attacker Advances                   0%                   42

Force Ratio…………Cases……Terrain…….Result

1.18 to 1.29 to 1        4             Nonurban   Defender penetrated

1.51 to 1.64               3             Nonurban   Defender penetrated

2.01 to 2.64               2             Nonurban   Defender penetrated

3.03 to 4.28               2             Nonurban   Defender penetrated

4.16 to 4.78               2             Urban         Defender penetrated

6.98 to 8.20               2             Nonurban   Defender penetrated

6.46 to 11.96 to 1      2             Urban         Defender penetrated

Now, my specific discussion on this is part of a three-page section on pages 209-211 called The Effect of Urban Terrain on Outcome. To quote from part of it:

The lack of any failed urban attacks is due to the favorable force ratios. The lowest force ratio of an urban attack is 1.72 to 1, and only four attacks are less than 2.00 to 1. Of the nine nonurban attacks between 1.71 and 2.00 to 1, only three failed. No attacks, urban or nonurban, executed with above 2.56 to 1 failed. There were a total of ten urban attacks made between 2.00 to 1 and 2.56 to 1 and nine nonurban attacks made in the same range. Two of the nonurban attacks in these cases failed.

This it appears that force ratios are a major factor in determining outcome. It does not appear that the difference between urban and nonurban terrain significantly influenced this result, nor can a difference be seen between rugged terrain and nonrugged terrain. Also the difference between rolling and mixed, rugged and mixed, or rugged and wooded terrain does not seem to have significantly influenced the outcomes. If a difference in the effect between rolling terrain and rugged terrain cannot be demonstrated, then the difference in effect between urban and nonurban terrain is also likely to be of the same order of effect, or less. However, the difference in terrain could affect combat power, and the difference caused by this effect could be 20 to 30 percent without it showing up in this analysis. Such small differences cannot be conclusively demonstrated given the small number of cases and the considerable variation found in this data.

Table 16.4. Summation of Force Ratios Compared to Outcomes, ETO

Force Ratio                                         Result

0.55 to 1.01 to 1.00                            Attack fails

1.15 to 2.56 to 1.00                            Attack may succeed

2.71 to 1.00 and higher                     Attack Advances

It is in the “attack may succeed” area where we may detect some differences caused by terrain effects. In the range of 1.15 to 2.56 to 1.00 we also found the statistics in table 16.5. For the urban versus nonurban cases, we found the statistics in table 16.6.

Table 16.5 Outcomes for attacks from 1.15 to 2.56 to 1.00

Cases            Attack Fails              Attack Advances             Defender Penetrated

55                   12 (21.82%)              35 (63.64%)                       8 (14.55%)

Table 16.6. Outcomes Based upon Terrain

                  Cases             Attack Fails         Attack Advances     Defender Penetrated

Urban        14                      0                         14                              0

Rolling        25                     6 (24.00%)         17                              2

Rugged       30                    6 (20.00%)          18                              6

Little can be concluded from this data, which appear to support a null hypothesis. That is, the terrain (be it urban vs. nonurban or rolling vs. rugged) has no significantly measurable included on the outcome of the battle.

Now, this is all kind of carefully worded to make sure I do not step beyond my data. Let me try to simplify this in three simple points:

1. Urban terrain does not favor the defender more so than other terrain (rolling or rugged). In fact, it appears less. 
2. Needless to say, the statement in the Modern War Institute article that “…ratio of 3:1 to have a reasonable chance of success” has little meaningful value. The attacker can be seen succeeding almost 80% of the time at ratios between 1.15 to 2.56 to 1. They reference the blog post that establishes this in their article.
3. The statement that “ratio as high as 6:1 is sometimes necessary to achieve success in urban operations because of the increased strength of the defense on urban terrain” is simply out there. We did three studies on urban warfare, using more cases than anyone else has done. While we did not establish what was the defensive value of urban terrain, it clearly was not massive.