Editing Little Boy (section)

===Assembly details===
Inside the weapon, the uranium-235 material was divided into two parts, following the gun principle: the "projectile" and the "target". The projectile was a hollow cylinder with 60% of the total mass ({{convert|38.5|kg|disp=sqbr}}). It consisted of a stack of nine uranium rings, each {{convert|6.25|in}} in diameter with a {{convert|4|in|adj=on}} bore in the center, and a total length of {{convert|7|in}}, pressed together into the front end of a thin-walled projectile {{convert|16.25|in}} long. Filling in the remainder of the space behind these rings in the projectile was a [[tungsten carbide]] disc with a steel back. At ignition, the projectile slug was pushed {{convert|42|in}} along the {{convert|72|in|mm|adj=mid|-long}}, {{convert|6.5|in|mm|adj=mid|-wide}} smooth-bore gun barrel. The slug "insert" was a 4-inch cylinder, 7 inches in length with a {{convert|1|in|adj=on}} axial hole. The slug comprised 40% of the total fissile mass ({{convert|25.6|kg|disp=or}}). The insert was a stack of six washer-like uranium discs somewhat thicker than the projectile rings that were slid over a 1-inch rod. This rod then extended forward through the tungsten carbide plug, impact-absorbing anvil, and nose plug backstop, eventually protruding out of the front of the bomb casing. This entire target assembly was secured at both ends with locknuts.<ref name=nukearchive>{{cite web |title=Nuclear Weapons Frequently Asked Questions, Section 8.0: The First Nuclear Weapons |first=Carey |last=Sublette |url=http://nuclearweaponarchive.org/Nwfaq/Nfaq8.html |access-date=29 August 2013}}</ref>{{sfn|Coster-Mullen|2012|pp=18–19, 27}}

When the hollow-front projectile reached the target and slid over the target insert, the assembled super-critical mass of uranium would be completely surrounded by a tamper and neutron reflector of tungsten carbide and steel, both materials having a combined mass of {{convert|2300|kg}}.{{sfn|Bernstein|2007|p=133}} [[Neutron initiator]]s inside the assembly were activated by the impact of the projectile into the target.{{sfn|Hoddeson|Henriksen|Meade|Westfall|1993|pp=263–265}}

[[File:Little Boy Internal Components.png|center]]