uranium-plutonium COBRA core was levitated in a type-D pit. COBRA was Los Alamos' most recent product of design work on the "new principles" of the hollow core. A copper pit liner encased within the weapon-grade plutonium inner capsule prevented DT gas diffusion into the plutonium, a technique first tested in Greenhouse Item. The assembled module weighed , measuring across. It was located at the end of the device, which, as seen in the declassified film, shows a small cone projecting from the ballistic case. This cone is the part of the paraboloid that was used to focus the radiation emanating from the primary into the secondary. Deuterium and lithium The device was called SHRIMP, and had the same basic configuration (radiation implosion) as the Ivy Mike wet device, except with a different type of fusion fuel. SHRIMP used lithium deuteride (LiD), which is solid at room temperature; Ivy Mike used cryogenic liquid deuterium (D2), which required elaborate cooling equipment. Castle Bravo was the first test by the United States of a practical deliverable fusion bomb, even though the TX-21 as proof-tested in the Bravo event was not weaponized. The successful test rendered obsolete the cryogenic design used by Ivy Mike and its weaponized derivative, the JUGHEAD, which was slated to be tested as the initial Castle Yankee. It also used a 7075 aluminium ballistic case 9.5 cm thick. Aluminium was used to drastically reduce the bomb's weight and simultaneously provided sufficient radiation confinement time to raise yield, a departure from the heavy stainless steel casing (304L or MIM 316L) employed by contemporary weapon-projects. The SHRIMP was at least in theory and in many critical aspects identical in geometry to the RUNT and RUNT II devices later proof-fired in Castle Romeo and Castle Yankee respectively. On paper it was a scaled-down version of these devices, and its origins can be traced back to the spring and summer of 1953. The United States Air Force indicated the importance of lighter thermonuclear weapons for delivery by the B-47 Stratojet and B-58 Hustler. Los Alamos National Laboratory responded to this indication with a follow-up enriched version of the RUNT scaled down to a 3/4 scale radiation-implosion system called the SHRIMP. The proposed weight reduction (from TX-17's to TX-21's ) would provide the Air Force with a much more versatile deliverable gravity bomb. The final version tested in Castle used partially enriched lithium as its