---
title: "Claim Ledger: The Planes That Didn't Come Back"
description: "Success stories and the antiques that outlasted the rest. Your evidence was filtered by what survived to reach you."
author: "Harry Floyd"
publication: "The Durability Curve"
canonical: "https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/"
essay: "https://durabilitycurve.com/blog/the-planes-that-didnt-come-back/"
published: "2026-09-09"
ledger_date: "2026-10-13"
claims: 7
removed_before_publication: 0
---

# Claim Ledger: The Planes That Didn't Come Back

*Success stories and the antiques that outlasted the rest. Your evidence was filtered by what survived to reach you.*

Essay: https://durabilitycurve.com/blog/the-planes-that-didnt-come-back/  
Ledger (canonical, cite this): https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/  
Published 2026-09-09 · last verified 2026-10-13

## The evidence, row by row

Labels: VERIFIED = checked against the primary source itself by a checker who did not draft the piece, usually with the exact words, where they sit and the date read · EXECUTED = a run or observation done for the piece (code, a query, a count, or a check made live in an app); the claim is what it returned; run records are not published · CHECKED = checked against its source by a separate checker in the older ledger format, which recorded no quote, locator or date · REPORTED = not verified word for word against a primary source (secondary, not openable in full, or supported only in part); the essay words it accordingly · STRUCK = drafted, checked and removed before publication · EXCLUDED = considered and deliberately left out.

### W1. Wald's work on aircraft vulnerability is a series of eight memoranda, originally published in 1943 by the Statistical Research Group at Columbia University for the National Defense Research Committee. Scope: these are the words of the abstract that the Center for Naval Analyses wrote for its 1980 reprint, not Wald's own.

- Status: VERIFIED (read 2026-10-13)
- Row link: https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/#c-W1
- Quote: a series of eight memoranda originally published by the Statistical Research Group at Columbia University for the National Defense Research Committee in 1943
- Source: Abraham Wald, A Method of Estimating Plane Vulnerability Based on Damage of Survivors (eight memoranda, 1943), reprinted by the Center for Naval Analyses as CRC 432, July 1980; abstract on the reprint's Report Documentation Page, Report Documentation Page, block 20 (Abstract), which follows printed p. 89 and is outside the body's page numbering (PDF p. 99). Block 18 on the same page lists the eight memo numbers.
- URL: https://www.cna.org/reports/1980/0204320000.pdf

### W2. Wald's method starts from two kinds of count: the total number of planes that took part in combat and, for each number of hits, the number of planes that took exactly that many hits and returned. Scope: the memoranda define their data in these terms and do not say who examined the aircraft or how the hits were recorded.

- Status: VERIFIED (read 2026-10-13)
- Row link: https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/#c-W2
- Quote: The total number N of planes participating in combat … planes that received exactly i hits but have not been downed, i.e., have returned from combat
- Source: Abraham Wald, A Method of Estimating Plane Vulnerability Based on Damage of Survivors, Part I, An Equation Satisfied by the Probabilities That a Plane Will Be Downed by i Hits (SRG memo 85), reprinted by the Center for Naval Analyses as CRC 432, July 1980, Part I, Introduction, printed p. 1 (PDF p. 10)
- URL: https://www.cna.org/reports/1980/0204320000.pdf

### W3. Wald names the gap in his own words: the share of planes that actually survived a given hit in a particular combat is unknown, because the distribution of hits on the planes that did not return is not known.

- Status: VERIFIED (read 2026-10-13)
- Row link: https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/#c-W3
- Quote: is unknown, since we do not know the distribution of hits on the planes that did not return
- Source: Abraham Wald, A Method of Estimating Plane Vulnerability Based on Damage of Survivors, Part VII, Miscellaneous Remarks (SRG memo 109), reprinted by the Center for Naval Analyses as CRC 432, July 1980, Part VII, remark 2 (Non-probabilistic interpretation of the results), printed p. 76 (PDF p. 85)
- URL: https://www.cna.org/reports/1980/0204320000.pdf

### W4. To estimate how vulnerable each part of the plane is, Wald's method needs a second input besides the damage on returning planes: how hits are distributed over the parts of the plane. He states that the two cannot both be estimated from the returning planes' damage alone, and he takes the hit distribution as known beforehand or as measured by firing dummy bullets.

- Status: VERIFIED (read 2026-10-13)
- Row link: https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/#c-W4
- Quote: it is impossible to estimate both … from the damage to returning planes only … can be assumed to be known a priori … or can be established experimentally by firing with dummy bullets
- Source: Abraham Wald, A Method of Estimating Plane Vulnerability Based on Damage of Survivors, Part V, Subdivision of the Plane into Several Equi-Vulnerability Areas (SRG memo 96), reprinted by the Center for Naval Analyses as CRC 432, July 1980, Part V, printed p. 57 (PDF p. 66). The two quantities are defined on printed p. 56 (PDF p. 65); the worked example sets the hit distribution equal to each part's share of the plane's area (printed p. 62, PDF p. 71).
- URL: https://www.cna.org/reports/1980/0204320000.pdf

### W5. In the worked example that closes Part V, a single hit on the engines is survived with probability .61 and downs the plane with probability .39; for the fuselage the figures are .95 and .05. Wald concludes that, for this example, the engine area is the most vulnerable. Scope: Wald calls the example hypothetical, so the figures illustrate the method and are not measurements from combat.

- Status: VERIFIED (read 2026-10-13)
- Row link: https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/#c-W5
- Quote: Engines .61 .39 … Fuselage .95 .05 … for the observed data of this hypothetical example, the engine area is the most vulnerable in the sense that a hit there is most likely to down the plane
- Source: Abraham Wald, A Method of Estimating Plane Vulnerability Based on Damage of Survivors, Part V, Subdivision of the Plane into Several Equi-Vulnerability Areas (SRG memo 96), reprinted by the Center for Naval Analyses as CRC 432, July 1980, Part V, Numerical Example, summary table and closing paragraph, printed p. 65 (PDF p. 74). The table's two figure columns are the probability of surviving a single hit and the probability of being downed by a single hit.
- URL: https://www.cna.org/reports/1980/0204320000.pdf

### W6. In the Part V worked example the engines are not free of hits on the planes that came back. Of the 202 hits counted on returning planes, 39 are on part 1, the engines (.193 of the total), and 78 are on part 2, the fuselage (.386). Scope: the figures are hypothetical; they show the engines hit less often than the fuselage, which is not the same as untouched.

- Status: VERIFIED (read 2026-10-13)
- Row link: https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/#c-W6
- Quote: The hits on the returning planes were distributed as follows … 1 39 .193 … 2 78 .386 … Total number of hits 202
- Source: Abraham Wald, A Method of Estimating Plane Vulnerability Based on Damage of Survivors, Part V, Subdivision of the Plane into Several Equi-Vulnerability Areas (SRG memo 96), reprinted by the Center for Naval Analyses as CRC 432, July 1980, Part V, Numerical Example, table of hits by part, printed p. 64 (PDF p. 73). Columns: part number, number of hits observed on part, ratio to total observed hits. Part 1 is the 2 engines and part 2 the fuselage, with shares of the plane's area of .269 and .346 (printed p. 63, PDF p. 72).
- URL: https://www.cna.org/reports/1980/0204320000.pdf

### W7. The memoranda's one statement about armour is that the conclusions drawn from the Part VIII vulnerability table, in which the plane is most vulnerable to a hit on the engine area when the type of bullet is not specified, can be used as guides for locating protective armour. Scope: the table comes from data Wald calls hypothetical; a search of the reprint's text finds armour mentioned in this sentence only, and the sentence makes no recommendation about any actual aircraft.

- Status: VERIFIED (read 2026-10-13)
- Row link: https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/#c-W7
- Quote: the hypothetical data would lead to the conclusion that the plane is most vulnerable to a hit on the engine area if the type of bullet is not specified … can be used as guides for locating protective armor
- Source: Abraham Wald, A Method of Estimating Plane Vulnerability Based on Damage of Survivors, Part VIII, Vulnerability of a Plane to Different Types of Guns (SRG memo 126), reprinted by the Center for Naval Analyses as CRC 432, July 1980, Part VIII, Comments on Results, printed pp. 88 and 89 (PDF pp. 97 and 98). The first part of the quote is on PDF p. 97; the armour clause is on PDF p. 98.
- URL: https://www.cna.org/reports/1980/0204320000.pdf

## Cite

- A claim: name the original source (and its locator) first, then the row it was checked in, e.g. "<source>, <locator>. Checked in: Claim Ledger, "The Planes That Didn't Come Back", The Durability Curve, row <id>, https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/#c-<id>."
- The essay: Floyd, Harry (2026). The Planes That Didn't Come Back. The Durability Curve. https://durabilitycurve.com/blog/the-planes-that-didnt-come-back/
- This ledger: Floyd, Harry (2026). Claim Ledger: The Planes That Didn't Come Back. The Durability Curve. https://durabilitycurve.com/claims/the-planes-that-didnt-come-back/
- Downloads: https://durabilitycurve.com/claims/the-planes-that-didnt-come-back.csv · https://durabilitycurve.com/claims/the-planes-that-didnt-come-back.json

Licence: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Reuse it, quote it or train on it, with credit to The Durability Curve and a link. Open to AI (robots.txt: search=yes, ai-input=yes, ai-train=yes).