Mk.8 Light Case (L.C. or Elsie or Little Child) (TX 8)

The Mk-8 was a derivative of the earlier "Little Boy" gravity bomb. On February 15, 1951 authorization was given by the AEC to develop the XW-8/Regulus warhead. Only one flight test was conducted, and the warhead work was suspended in May 1955, when the Navy decided to investigate thermonuclear warheads for Regulus.

The bomb contained the same gun-type fuse as the Mark 1 "Little Boy," in which two subcritical masses (each less than what is required to cause a chain reaction) of nuclear material are placed at opposite ends of a long tube. To trigger detonation, an explosive charge at one end of the tube propels one of the nuclear masses down the pipe into the other subcritical mass, hence creating a supercritical mass (a quantity sufficient to cause a nuclear chain reaction) and resulting in a massive release of energy. This type of trigger makes for a simpler and more reliable type of bomb.

The cannon charges had many advantages and were distinguished by simplicity, reliability, compactness. The greatest interest in the development of light tactical cannon-type weapons was demonstrated by the Army, the Navy, and the Marine Corps. The Air Force and specialists of Los Alamos, on the contrary, considered the manufacture of cannon charges as a waste of precious damage-235. Nevertheless, after the tests of 1946 in Bikini, which showed a great efficiency of the underwater nuclear explosion, the fleet ordered a Los Alamas laboratory project for a lightweight, in comparison with the "Little Boy," a cannon-type bomb.

This project was named Elsie (LC, Light Case). Gradually, the main purpose of Elsie was not an underwater target, but an underground nuclear explosion. Such an explosion was more effective than air for many point, heavily fortified targets: bridges, submarine shelters, command posts, airfields, ships in the harbor, etc. The targets were destroyed by seismic action or simply fell into the formed funnel. Similar ideas have previously formed the basis of the most powerful non-nuclear bombs: English "Tollboy" and "Grand Slam", as well as American "Amazon" and T-10.

Elsie's main developer was the Navy's Bureau of Ordnance (BuOrd), the Los Alamos Laboratory was responsible for the new neutron initiator. Because of the tense situation with the accumulation of fissile materials, it was possible to make a new bomb, designated Mk.8, only in January 1951, and its value reached $3,127,600.

Mk.8 was conceived and manufactured at the initiative of the Navy for the arming of the strategic deck bombers Lockheed P2V-3C Neptune. However, later it became interested in the command of the Air Force. Specialists of the Air Force came to the conclusion that for a sure defeat of various targets, the bombs of an underground explosion should account for about 5% of the total nuclear arsenal. The first Mk.8 went into service in April 1952. In total from November 1951 to my 1953 about 40 Mk.8 bombs of two modifications were made: Mod.0 and Mod.1. They were in service until August 1957, when they were replaced by Mk.11 bombs.

The Bomb Mk.8 was the development of "Little Boy", but much lighter and more compact it. A durable steel case with a diameter of only 370 mm resembled a torpedo. The mass of the bomb was from 1465 to 1490 kg. The cannon nuclear charge with a 3-inch barrel was similar to the "Little Boy" charge, but it was deployed 180 °. This was done to facilitate loading, including in flight, although from the point of view of centering, the current layout is less advantageous. In addition, due to the fact that the Mk.8 gun fired at the tail of the bomb, the projectile was not moved toward the target under the influence of axial overloads, which occur when striking the ground.

The TNT equivalent of the Mk.8 bomb was 15-20 kt. But each bomb required about 50 kg of uranium-235 90 percent enrichment.

The bomb Mk.8 had a very simple system of detonation, generally without electrical circuits. To detonate the powder charge, three pyrotechnic detonators of delayed action, installed one in the bow and two in the middle, on both sides of the hull, served. Slowdown - from 60 to 180 seconds - was installed from the aircraft before discharge. The fuses were lit at the time of separation from the aircraft. Due to this scheme of the detonation system, the aircraft always had time to escape from the epicenter of the explosion, so the Mk.8 bomb could be dropped from any, including small, heights, its light-weight AD-1 "Skyraider" attack helicopters could be carrying it. Before the explosion, the Mk.8 bomb went deep into the ground to a depth of 10 m (sand) to 30 m (soft clay).

According to one source, the Mark 8, an early penetration bomb, could penetrate 22 feet of reinforced concrete, 90 feet of hard sand, 120 feet of clay, or 5 inches of armor plate before detonating. ["Weapon Design - We've Done a Lot but We Can't Say Much," by Carson Mark, Raymond E. Hunter, and Jacob J. Wechsler LOS ALAMOS SCIENCE Winter/Spring 1983]. According to another source, the Mk-8 could penetrate up to 40 ft of sand, 60 ft of loam and 100 ft of clay [US Nuclear Weapons: The Secret History by Chuck Hansen, Orion, 1988, p. 139-141].

Mk.8 had two main modifications. Mk.8 Mod.0 was intended, basically, for the internal suspension in the bomb bay. Bomb, a uranium shell, a powder charge and a cannon with a detonator were fixed in a special holder T-28. After takeoff, one of the crew members in the bomb bay manually loaded the gun. But this operation took about 18 minutes.

The T-28 holder with the Mk.8 Mod.0 bomb could also be installed in an external suspension. At the same time, the plane took off with a charged bomb, but due to the exceptional stability of the Mk.8 blasting system to shock loads, it was considered quite safe. Externally, the Mk.8 Mod.0 bomb was different from Mod. 1 blunt nose. Its length was 2950 mm. Bomb Mk.8 Mod.1 was located, as a rule, but external suspension. The attachment points were unified with the bomb Mk.7. Mk.8 Mod. 1 had a pointed nose fairing, under which was placed the mechanism of automatic loading of the gun. Therefore, the length of the bomb was 3350 mm. In 1955, all the Mk.8 Mod.1 bombs were redesigned in Mod.2 and Mod.3. In 1951-1955, attempts were made to use the nuclear charge Mk.8 at the head of the Regulus cruise missile.

China Lake did not work on nuclear warheads, but supported a number of special weapon programs during the 1950s, when the military's focus was largely on nuclear weapons, with safety evaluations, component and shape testing, and component development. China Lake redesigned the Elsie (TX 8/TX 11) penetrator weapon.

The AD-4B was the first Navy fighter/attack aircraft with the low altitude bombing LABS system with wiring and controls for fuzing and arming. The center line rack that could carry the 1680 pound MK-7. Also carried was the Navy developed 3,250 pound MK-8 with delayed action detonation instead of the air burst of earlier weapons, to attack underground facilities.