Little Boy
Enable an agent to identify records and artifacts attributed to Little Boy, distinguish the historical weapon from representations, assess evidential and physical state, and determine appropriate research or custodial actions.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an agent to identify records and artifacts attributed to Little Boy, distinguish the historical weapon from representations, assess evidential and physical state, and determine appropriate research or custodial actions.
Little Boy is the United States Mark I gun-type fission weapon that assembled a supercritical mass by firing a subcritical projectile of highly enriched uranium-235 into a subcritical uranium target, and is the nuclear explosive detonated in combat over Hiroshima on 6 August 1945.
It can be Resolve a Little Boy mention to the appropriate historical referent or flag ambiguity.; Compare an attributed artifact with documented external appearance and provenance.; Link the weapon to independently modeled production, delivery, and detonation events.; Evaluate whether a source supports claims about the original weapon, a design, or a particular exhibit.; Prepare qualified catalogue descriptions and route artifact access or conservation requests to the documented custodian..
Distinguishing features
Require historical attribution connecting the name to the Hiroshima weapon; a matching phrase alone cannot establish identity. [U.S. Navy historical record](https://www.history.navy.mil/content/history/museums/nmusn/explore/photography/wwii/wwii-pacific/bombardment-japan/bombs-atomic/little-boy-hiroshima.html)
Use the documented uranium gun-type classification as a broad discriminator from other atomic weapon designs, without recording construction parameters. [National Park Service](https://www.nps.gov/mapr/learn/atomic-weapons.htm)
Distinguish an individual-weapon claim from a design-type reference: a Little Boy label does not establish that an object is the weapon used at Hiroshima.
Require object-specific provenance for a surviving casing, component, or display artifact; silhouette and paint scheme establish resemblance, not historical authenticity.
Reject an intact surviving-original attribution unless it resolves the contradiction with the documented detonation of the Hiroshima weapon. [U.S. Navy historical record](https://www.history.navy.mil/content/history/museums/nmusn/explore/photography/wwii/wwii-pacific/bombardment-japan/bombs-atomic/little-boy-hiroshima.html)
Scope
+ Resolution of the name Little Boy to the historical weapon, with explicit uncertainty about registry intent.
+ Distinction between the individual weapon, its design designation, attributed components, and museum representations.
+ Non-operational physical characteristics used to identify and compare attributed objects.
+ Documented lifecycle, custody, and relationship to the Hiroshima bombing.
+ Evidence quality, artifact condition, and constraints on research, conservation, and display.
- Children or people described as a little boy.
- Nuclear weapon construction, assembly, arming, deployment, or performance optimization.
- The Manhattan Project as an organization and production programme.
- The delivery aircraft, crew, and mission as independently modeled entities.
- Hiroshima casualties, environmental consequences, and remembrance practices as independently modeled events and social phenomena.
- Other nuclear weapons and independently catalogued museum replicas.
Characteristics
- Referent class
- historical individual | design reference | attributed component | replica | representation | unresolved Prevents transferring the identity or properties of the Hiroshima weapon to everything carrying its name.
- Historical attribution
- Claimed relationship to Little Boy, with supporting record, date, and confidence Separates documented association from appearance-based or promotional attribution.
- Broad weapon classification
- Documented historical classification; conflicting attribution; unknown Supports recognition and comparison without describing weapon engineering.
- External envelope
- Overall length and maximum external diameter in metres; identify measured object, source, and uncertainty Helps compare photographs and display artifacts while preventing replica measurements from becoming original-weapon specifications.
- Historical lifecycle state
- Documented stage or terminal event, with date and evidence; unknown where unsupported Keeps historical states separate from the present condition of associated artifacts.
- Artifact authenticity and alteration
- Documented original material | restored | reconstructed | reproduced | mixed | unresolved Determines what an artifact can substantiate about the historical weapon.
- Present custody
- Custodian and accession record for an identified surviving artifact, with effective date Supports access and conservation decisions without assigning present custody to the detonated weapon.
- Artifact hazard assessment
- Not assessed | documented assessment available | restrictions recorded; assessor, date, and scope required Prevents inferring safe handling or hazardous contents from a museum label or historical weapon classification.
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 6 bundles · 11 layers · 18 findings · 28 questions.
Named weapon identity Establish what the registry name denotes and how related objects refer to it.
Little Boy can identify a historical individual or appear on records and exhibits describing a weapon type.
Registry referent
Resolve the missing registry definition before treating the interpretation as settled.
Intended Little Boy
Record the evidence for interpreting this entry as the historical weapon and preserve unresolved alternatives.
- What registry context establishes that Little Boy denotes the historical weapon? definition
- Does an existing world model already own this concept and therefore require a link instead of a second publication? boundary
Individual and representations
Separate references to the historical individual from references to designs and associated artifacts.
Attribution role
Qualify each related record as an individual-weapon claim, type reference, component attribution, or representation.
- Does this record describe the Hiroshima weapon itself, a design, a component, or a replica? definition
- Which provenance establishes that relationship beyond the shared name? provenance
Historical physical recognition Support identification through broad classification and documented exterior evidence.
Recognition requires distinguishing Little Boy from other weapons and from inaccurate representations without modeling construction.
Classification evidence
Capture sourced historical classification at a non-operational level.
Weapon type attribution
Associate broad classification claims with the exact referent described by their source.
- Which authoritative source establishes the broad weapon classification for this referent? provenance
- Does a conflicting classification indicate a misidentified weapon or a misread source? boundary
Exterior comparison
Compare observable form while distinguishing historical evidence from exhibit modifications.
Documented exterior
Record overall outline, tail appearance, visible markings, and external measurements only with their object and date.
- Were these external measurements taken from the historical weapon, a drawing, or a particular replica? measurement
- Which photographs or conservation records establish whether the visible finish and markings are historical or later additions? provenance
Hiroshima lifecycle Track the named weapon through documented historical stages and its terminal event.
The weapon's historical existence must remain distinct from the later existence of objects exhibited under its name.
Pre-event continuity
Establish continuity between records attributed to the weapon before its use.
Historical record chain
Link documented production, custody, and transport references without assuming every similarly named item is the same object.
- Which records establish continuity of the individual weapon across documented custody changes? provenance
- Where do records concern separate components or test articles instead of the historical individual? boundary
Terminal event link
Connect the historical object to its use while leaving the event's wider consequences to neighbouring models.
Detonation and identity
Record the sourced terminal event and use it to constrain later claims of survival or custody.
- Which event record establishes the date, place, and identity of the weapon used? provenance
- Does a later survival claim concern an attributed fragment, another article, or a representation? boundary
Attributed artifact state Assess the authenticity and condition of separately identified objects associated with Little Boy.
A display object can support historical interpretation while having a different material history and present state.
Material authenticity
Establish what an associated artifact physically contains and what has been altered.
Original and reproduced material
Distinguish documented period material from replacement parts, reconstruction, and uncertain attribution.
- What accession or conservation evidence identifies this artifact as period material, reproduction, or a mixture? provenance
- Which alterations limit using its present appearance as evidence for Little Boy? boundary
Custodial condition
Record condition and access constraints for the specific surviving artifact.
Artifact-specific access
Base inspection, handling, and conservation decisions on current custodian records and assessments.
- What dated condition and hazard assessments apply to this specific artifact? provenance
- What inspection, photography, handling, or conservation actions does its custodian permit? action
Historical claim discipline Control how Little Boy claims are supported, qualified, and presented.
Historical specifications, exhibit descriptions, and event estimates can concern different referents and levels of certainty.
Source applicability
Evaluate whether evidence supports the particular object and historical stage being described.
Claim-to-referent match
Keep source scope, uncertainty, and conflicting accounts attached to individual claims.
- Does the source describe the Hiroshima weapon, a general design specification, or an exhibit? provenance
- When sources disagree, can the difference be explained by referent, measurement basis, or historical stage? measurement
Responsible description
Produce historically grounded descriptions with explicit boundaries around event interpretation.
Catalogue claim boundaries
Separate object identification from claims about casualties, strategic necessity, and historical responsibility.
- Which statements require links to bombing, casualty, or historical-interpretation models rather than attributes of the weapon? boundary
- What qualifications must accompany a catalogue description so readers can distinguish established identity from disputed attribution? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Combat article used at Hiroshima (the unit commonly designated L-11)
- 1945 inert and ballistic test drop units used to prove the casing and release sequence
- Post-war Mark I stockpile weapons (a small number, withdrawn by the early 1950s because the gun-type layout was not one-point safe)
- Inert museum and display casings that reproduce the external form without nuclear components
- Which of these kinds and varieties hold for the sense of Little Boy this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q105046 - Item for the Little Boy / Mark I gun-type uranium bomb.
- U.S. nuclear mark number - Mk I (Mark 1) - Service designation of the Little Boy design.
- Manhattan Project code name - Little Boy - Internal name adopted after the longer plutonium gun (Thin Man) was cancelled.
- Combat unit designation - L-11 - Unit number commonly assigned to the Hiroshima combat article.
- Which of these identifiers and schemes hold for the sense of Little Boy this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Atomic Energy Act of 1946 (U.S. Congress) - created the Restricted Data category covering nuclear-weapon design information.
- Atomic Energy Act of 1954 (U.S. Congress) - continuing statutory control of nuclear explosive design, materials, and information.
- Treaty on the Non-Proliferation of Nuclear Weapons, 1968 (depositary states; IAEA safeguards system) - governs later civilian HEU and bars new nuclear-weapon states from devices of this class.
- U.S. Department of Energy / NNSA classification practice for nuclear-weapon design - still restricts detailed internal drawings and specifications of gun-type assemblies.
- IAEA nuclear security guidance on highly enriched uranium (e.g. INFCIRC/225 series) - physical protection of the material class Little Boy used, not of the 1945 artifact itself.
- Which of these standards and regulation hold for the sense of Little Boy this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Single combat employment: airburst over Hiroshima from the B-29 Enola Gay of the 509th Composite Group on 6 August 1945.
- Inert practice drops from Tinian in July-August 1945 to rehearse release, ballistics, and fuzing of the elongated casing.
- Brief postwar U.S. stockpile of Mark I gun-type bombs, then withdrawal once safer implosion weapons were available.
- Museum display of empty casings and scale models as the canonical gun-type uranium bomb.
- Reference case in nonproliferation analysis for a technically simple HEU gun-assembly path.
- Which of these real-world use hold for the sense of Little Boy this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Overall length - about 3.00 - m
- Maximum diameter - about 0.71 - m
- All-up mass - about 4400 - kg
- Nuclear yield - 12-18 (modern consensus near 15) - kt TNT equivalent
- HEU mass in the pit/projectile-target system - about 64 - kg
- Average U-235 enrichment of that HEU - about 80 - % U-235
- Burst height over Hiroshima - 580-600 - m
- Which of these typical measurements hold for the sense of Little Boy this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Not one-point safe: a crash, fire, or unintended propellant burn can drive the projectile into the target and produce nuclear yield.
- Accidental criticality while loading or inserting the projectile and target.
- Fizzle (low yield) if the gun assembly is too slow, though this risk is much smaller with U-235 than it was for a plutonium gun.
- In-flight insertion or arming failure (safety plugs, fuzes, or the cordite gun charge) leaving a dud.
- Weapon effects on people and the city: blast, thermal pulse, prompt ionizing radiation, and residual contamination.
- Proliferation hazard: a gun-type HEU device is the least demanding nuclear-explosive architecture, so remaining design knowledge and HEU stocks are treated as high-risk.
- Which of these failure modes and hazards hold for the sense of Little Boy this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- In Japanese the weapon is リトルボーイ and is tied specifically to Hiroshima; Nagasaki is associated with Fat Man, not Little Boy.
- Little Boy was an Allied/Manhattan Project nickname, not a Japanese wartime designation of the object that was dropped.
- Some languages calque the name (for example French Petit Garçon); technical and museum practice usually keeps the English code name.
- Outside Japan, popular accounts often swap Little Boy and Fat Man or treat both as generic "the atomic bomb."
- Which of these regional variation hold for the sense of Little Boy this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Fat Man - Plutonium implosion weapon with a rounded casing used at Nagasaki; Little Boy is an elongated U-235 gun-type assembly and was not implosion-initiated.
- Thin Man - Cancelled plutonium gun-type predecessor, longer than Little Boy and abandoned because Pu-240 spontaneous fission made a slow gun assembly unsafe.
- Gadget (Trinity device) - The July 1945 New Mexico test article was a plutonium implosion device, not an air-dropped uranium gun bomb.
- Pumpkin bomb - Conventional high-explosive practice bomb with Fat Man ballistics; it is not a Little Boy casing and contains no nuclear assembly.
- The Hiroshima bombing (the event) - The raid, casualty, and city-destruction event is not the same object as the Mark I article; the weapon is the hardware that produced that burst.
- Which of these neighbouring kinds and how to tell them apart hold for the sense of Little Boy this model covers, and on what evidence? provenance
Sources
- The Making of the Atomic Bomb - Manhattan Project origin of the gun-type uranium design, the combat drop from Enola Gay, and the distinction from the plutonium implosion path.
- The Yields of the Hiroshima and Nagasaki Nuclear Explosions (LA-8819) - Technical yield estimates for the Hiroshima burst, typically cited near 15 kt TNT equivalent.
- Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943-1945 - Los Alamos design history of the uranium gun assembly, the abandonment of Thin Man, and why Little Boy used HEU rather than plutonium.
- Atom Bombs: The Top Secret Inside Story of Little Boy and Fat Man - Physical dimensions, HEU mass and layout, unit designations, and the distinction between combat, test, and casing hardware.
- U.S. Nuclear Weapons: The Secret History - Mark I designation, the small postwar stockpile, and early retirement on safety grounds.
- The Effects of Nuclear Weapons - Blast, thermal, and ionizing-radiation effects that follow a low-kiloton airburst of this class.
- Little Boy - Widely repeated identifiers, dimensions, Hiroshima employment facts, and the conventional contrast with Fat Man.
What the second pass must settle
- Does the registry intend the individual Hiroshima weapon, the named weapon design, or another referent entirely?
- Does an existing world model already cover the intended concept, requiring this entry to link to it?
- Which authoritative records establish individual identity across production, transport, and use without conflating separate components or test articles?
- Which associated artifacts have documented provenance, and what portions of each are period material, restoration, or reproduction?
- Which published physical descriptions apply specifically to the historical weapon, and which describe design specifications or later exhibits?