Castle Romeo Castle Romeo was the code name given to one of the tests in the Operation Castle series of American nuclear tests . It was the first test of the TX - 17 thermonuclear weapon ( initially the " emergency capability " EC - 17 ) , the first deployed U . S . thermonuclear bomb . The so - called " runt " device was a weaponized " dry " fusion bomb , using lithium deuteride fuel for the fusion stage of a " staged " fusion bomb , unlike the cryogenic liquid deuterium of the first - generation Ivy Mike fusion device . Similar to the " Shrimp " device tested shortly before , in the Castle Bravo test , it differed from that device in using lithium deuteride derived from natural lithium ( a mixture of Lithium - 6 and Lithium - 7 isotopes , with 7 . 5 % of the former ) as the source of the tritium and deuterium fusion fuels , as opposed to the relative high enrichment level of lithium ( approximately 40 % Lithium - 6 ) deuteride used in Bravo . It was detonated on March 27 , 1954 , after several delays ( which played havoc with the planned experimental measurements program ) at Bikini Atoll of the Marshall Islands , on a barge moored in the middle of the crater from the Castle Bravo test . It was the first such barge - based test , a necessity that had come about because the powerful thermonuclear devices completely obliterated the small islands on which they were set off . Like the Bravo test , it " ran away " and produced far more than its predicted yield , and for the same reason — an unexpected participation of the common Lithium - 7 isotope in fusion reactions . Although it had been predicted to produce a yield of 4 megatons with a range of 1 . 5 to 7 megatons ( before the results of the Bravo test caused an upgrade in the estimates , it had originally been estimated to produce 3 – 5 megatons ) , it actually produced a yield of 11 megatons , the third largest test ever conducted by the U . S . Like the Ivy Mike and Castle Bravo tests , a large percentage of the yield was produced by fast fission of the natural uranium " tamper " ; 7 megatons of the yield were from this source . Deployment . This became the first air - droppable thermonuclear device , the EC - 17 , of which only 5 were made and the first deployable staged radiation implosion Teller - Ulam thermonuclear weapon . This evolved into the Mk 17 of which 200 were made . Both of these were huge devices , weighing 39 , 000 and 42 , 000 pounds respectively . As a result they were only capable of being carried by the B - 36 . They were also some of the largest yield devices deployed by Strategic Air Command — the EC - 17 giving around 10 Mt and the Mk17 between 11 and 15 Mt . They were all out of service by August 1957 . Fireball in popular culture . One particular image of the Castle Romeo fireball ( above , at right ) has been one of the most highly reprinted images of a nuclear explosion , often serving as a stand - in for nuclear weapons in general for news stories , book covers , magazine articles , and even congressional reports ( such as the Cox Report ) , likely because of its threatening appearance and extreme red , orange , and yellow hues . In many cases the fact that the explosion is of a US megaton - range weapon has not prevented it to be used to represent the arsenals of other states or weapons of far lower yields , which would have a very different appearance . One prominent usage is as the backdrop for heavy metal band Megadeth ' s greatest hits compilation " " . The image of Castle Romeo was also used on the cover of the New York hardcore music pioneers Cro - Mags debut album " The Age of Quarrel " . It is also featured on the title screen of Team17 ' s turn - based artillery game " Worms Armageddon " . The Castle Romeo photos are sometimes confused with that of Castle Bravo ; the two nuclear blasts looked very similar , and they were both conducted in the same location .