Operation Sandstone Operation Sandstone was a series of nuclear weapon tests in 1948 . It was the third series of American tests , following Trinity in 1945 and Crossroads in 1946 , and preceding Ranger . Like the Crossroads tests , the Sandstone tests were carried out at the Pacific Proving Grounds , although at Enewetak Atoll rather than Bikini Atoll . They differed from Crossroads in that they were conducted by the Atomic Energy Commission , with the armed forces having only a supporting role . The purpose of the Sandstone tests was also different : they were primarily tests of new bomb designs rather than of the effects of nuclear weapons . Three tests were carried out in April and May 1948 by Joint Task Force 7 , with a work force of 10 , 366 personnel , of whom 9 , 890 were military . The successful testing of the new cores in the Operation Sandstone tests rendered every component of the old weapons obsolete . Even before the third test had been carried out , production of the old cores was halted , and all effort concentrated on the new Mark 4 nuclear bomb , which would become the first mass - produced nuclear weapon . More efficient use of fissionable material as a result of Operation Sandstone would increase the U . S . nuclear stockpile from 56 bombs in June 1948 to 169 in June 1949 . Origins . Nuclear weapon s were developed during World War II by the Manhattan Project , which created a network of production facilities , and the weapons research and design laboratory at the Los Alamos National Laboratory . Two types of bombs were developed : the Mark I Little Boy , a gun - type fission weapon using uranium - 235 , and the Mark III Fat Man , an implosion - type nuclear weapon using plutonium . These weapons were not far removed from their laboratory origins . A great deal of work remained to improve ease of assembly , safety , reliability and storage before they were ready for production . There were also many improvements to their performance that had been suggested or recommended during the war that had not been possible under the pressure of wartime development . Norris Bradbury , who replaced Robert Oppenheimer as director at Los Alamos , felt that " we had , to put it bluntly , lousy bombs . " Plutonium was produced by irradiating uranium - 238 in three 250 MW nuclear reactors at the Hanford site . In theory they could produce of plutonium per megawatt - day , or about per month . In practice , production never approached such a level in 1945 , when only between was produced per month . A Fat Man core required about of plutonium , of which 21 % fissioned . Plutonium production fell off during 1946 due to swelling of the reactors ' graphite neutron moderators . This is known as the Wigner effect , after its discoverer , the Manhattan Project scientist Eugene Wigner . These reactors were also required for the production of polonium - 210 by irradiation of bismuth - 209 , which was used in the modulated neutron initiator s , a critical component of the nuclear weapons . Some of bismuth - 209 had to be irradiated for 100 days to produce 600 curies of polonium - 210 , a little over . Because polonium - 210 has a half - life of only 138 days , at least one reactor had to be kept running . The oldest unit , B pile , was therefore closed down so that it would be available in the future . Investigation of the problem would take most of 1946 before a fix was found . Uranium - 235 was produced from enrichment of natural uranium at the Oak Ridge National Laboratory . Improvements in the processes and procedures of the electromagnetic and gaseous isotope separation between October 1945 and June 1946 led to an increase in production to around of uranium - 235 per month , which was only enough for one of the very wasteful Little Boys . A Fat Man was 17 . 5 times as efficient as a Little Boy , but a ton of uranium ore could yield eight times as much uranium - 235 as plutonium , and on a per - gram basis , plutonium cost somewhere between four and eight times as much to produce as uranium - 235 , which at this time cost around $ 26 per gram . Weapon development 1945 – 48 . The objectives of the Sandstone series of tests were to : Levitation meant that instead of being immediately inside the tamper , there would be an air gap between the tamper and the core , which would be suspended inside on wires . This would allow the tamper to gain more momentum before striking the core . The principle was similar to swinging a hammer at a nail . In order for this to work outside the laboratory , the wires had to be strong enough to withstand being dropped from an aircraft , but thin enough to not disturb the spherical symmetry of the implosion . The Theoretical Division at Los Alamos , known as T Division , had run computer calculations on the levitated core as early March 1945 . The use of the levitated core had been proposed during the planning for Operation Crossroads , but it had been decided instead to use the existing solid core " Christy " design . This was named after its designer , Robert Christy . For Sandstone , however , it was decided that at least two of the three tests would use levitated cores . The motivation behind the composite core was to make better use of the available fissionable material . The use of uranium - 235 in an implosion weapon instead of the inefficient gun type Little Boy was an obvious development . However , while plutonium was more expensive and harder to produce than uranium - 235 , it fissions faster , because it makes better use of the neutrons its fission produces . On the other hand , the slower reaction of uranium - 235 permits the assembly of super - critical masses , making it theoretically possible to produce weapons with high yields . By July 1945 , Oppenheimer and Groves were considering using both materials in a composite core containing of plutonium and of uranium - 235 . The composite cores became available in 1946 . Los Alamos ' priority then became the development of an all - uranium - 235 core . By January 1948 the national stockpile contained 50 cores , of which 36 were composite Christy cores , nine were plutonium Christy cores , and five were composite levitated cores . Testing the new levitated , composite and uranium - 235 cores would require at least three test firings . More efficient weapons would require less efficient initiators . This meant that less polonium would be required . At the time of Sandstone , the national stockpile of polonium - beryllium initiators consisted of 50 A - Class initiators , with more than 25 curies of polonium , and 13 B - Class initiators with 12 to 25 curies . During Sandstone , at least one test would be conducted with a B - Class initiator . Preparations . Organization . The tests were authorized by President Harry S . Truman on 27 June 1947 . The Atomic Energy Commission ' s Director of Military Applications , Brigadier General James McCormack and his deputy , Captain James S . Russell , met with Bradbury and John Manley at Los Alamos on 9 July to make arrangements for the tests . They readily agreed that they would be scientific in nature , with Los Alamos supplying the technical direction and the armed forces providing supplies and logistical support . The cost of the tests , around $ 20 million , was divided between the Department of Defense and the Atomic Energy Commission . Lieutenant General John E . Hull was designated as test commander . Rear Admiral William S . Parsons and Major General William E . Kepner reprised their Operation Crossroads roles as deputy commanders . Joint Task Force 7 was formally activated on 18 October 1947 . As its commander , Hull was answerable to both the Joint Chiefs of Staff and the Atomic Energy Commission . Joint Task Force 7 consisted of 10 , 366 personnel , 9 , 890 of them military . Its headquarters consisted of about 175 men , of whom 96 were on board the . The rest were accommodated on the , and . A special division of the Los Alamos National Laboratory , known as J Division , was created specifically to manage nuclear testing . An Atomic Energy Commission group ( Task Group 7 . 1 ) was responsible for preparing and detonating the nuclear weapons , and conducting the experiments . It consisted of some 283 scientists and technicians responsible for nuclear tests from J Division , the Armed Forces Special Weapons Project , the Naval Research Laboratory , the Naval Ordnance Laboratory , Argonne National Laboratory , the Aberdeen Proving Ground , the Atomic Energy Commission , Edgerton , Germeshausen & Grier , and other agencies . Each dealt with a different aspect of the tests . The Naval Ordnance Laboratory handled the blast measurement tests , while the Naval Research Laboratory conducted the radiation measurement experiments , and Argonne National Laboratory did gamma ray measurements . Edgerton , Germeshausen , and Grier were contractors hired to design and install the timing and firing systems . Seven experimental weapon assemblies and six cores were delivered to San Pedro , California , and loaded on the weapon assembly ship USS " Curtiss " , in February 1948 , but the Atomic Energy Commission only gave permission for the expenditure of three cores in the tests . Ships . The naval forces were organized as Task Group 7 . 3 . It consisted of : Source : Berkhouse " et al " , " Operation Sandstone " , p . 40 Civil affairs . In September 1947 , Hull , Russell , who was designated test director on 14 October , and Joint Task Force 7 ' s scientific director , Darol K . Froman from the Los Alamos Laboratories , set out out with a group of scientists and military officers to examine various proposed test sites in the Pacific . Enewetak Atoll was chosen as the test site on 11 October . The island was remote , but with a good harbor and an airstrip . It also had ocean currents and trade winds that would carry fallout out to sea , an important consideration in view of what had happened at Bikini Atoll during Operation Crossroads . As the Trust Territory of the Pacific Islands was a United Nations trust territory administered by the United States , the United Nations Security Council was notified of the upcoming tests on 2 December . The atoll was inhabited by the dri - Enewetak , who lived on Aomon , and the dri - Enjebi , who lived on Bijire . Their original homes had been on Enewetak and Enjebi , but they had been moved during the war to make way for military bases . The population , about 140 in number , had been temporarily relocated to Meck Island during Operation Crossroads . This time , Ujelang Atoll , an uninhabited atoll southwest of Enewetak , was selected as a relocation site . A Naval Construction Battalion group arrived there on 22 November to build accommodation and amenities . The military authorities met with the local chiefs on 3 December , and they agreed to the relocation , which was carried out by by 20 December . An LST and four C - 54 aircraft were placed on standby to evacuate Ujelan in case it was affected by fallout , but were not required . Unlike the Crossroads tests , which were conducted in the media spotlight , the Sandstone tests were carried out with minimal publicity . On 15 April , there was still discussion in Washington about whether or not there should be any public announcement of the tests at all . Hull opposed making any announcement until after the series was completed , but the AEC commissioners felt that the news would leak out , and the United States would look secretive . It was therefore decided to make a last minute announcement . There was no announcement of the purpose of the tests , and only cursory press releases . On 18 May , after the series was over , Hull held a press conference in Hawaii , but only permitted the media to quote from written statements . Construction . Enjebi , Aomon , and Runit Islands were cleared of vegetation and graded level to make it easier to install the required instrumentation , and a causeway was built between Aomon and Bijire so the instrument cables could be run from the test tower on Aomon to the control station on Bijire . The detonations were ordered so that later test areas would suffer minimal fallout from the earlier shots . The Army component , Task Group 7 . 2 , was responsible for construction work . It consisted of the 1220th Provisional Engineer Battalion , with the 1217th and 1218th Composite Service Platoons , the 18th Engineer Construction Company and 1219th Signal Service Platoon ; Companies D and E of the 2nd Engineer Special Brigade ' s 532nd Engineer Boat and Shore Regiment ; the 461st Transportation Amphibious Truck Company ; 854th Transportation Port Company ; 401st CIC Detachment ; and the Naval Shore Base Detachment . Operations . As in Operation Crossroads , each detonation was given its own code name , taken from the Joint Army / Navy Phonetic Alphabet . All used modified Mark III assemblies , and were detonated from towers . The timing of the detonations was a matter of compromise . The gamma ray measurement experiments required darkness , but the B - 17 drones that would sample the clouds needed daylight to control them . As a compromise , the Sandstone detonations all took place shortly before dawn . The X - Ray nuclear device used a levitated composite core . It was detonated on Enjebi just before sunrise at 06 : 17 on 15 April 1948 , with a yield of 37 kilotons . The efficiency of utilization of the plutonium was about 35 % ; that of the uranium - 235 was 25 % or more . This was somewhat higher than Los Alamos ' prediction . Observers watching from ships in the lagoon saw a brilliant flash and felt the radiant heat . A condensation cloud in diameter quickly enveloped the fireball , which glowed within the cloud . It took 45 to 50 seconds for the thunderous roar of the explosion to reach the observers . About 20 minutes later , " Bariko " launched a helicopter to check on the cable winch which was to collect samples . It also lowered boats to test radioactivity levels in the lagoon . B - 17 pilotless drone aircraft were flown through the clouds , and a drone light tank was used to recover soil samples from the crater . Unfortunately , it became bogged and had to be towed out ten days later . The Yoke nuclear device used a levitated all - uranium - 235 core . It was detonated on Aomon just before sunrise on 1 May 1948 at 06 : 09 , a day late due to unfavorable winds . The observers saw a similar flash and felt the same heat as the X - Ray blast , but the wide condensation cloud was larger , and the sound of the explosion more forceful . One observer likened it to the sound of " a paper bag which is forcefully burst in a small room " . They were correct : its yield of 49 kilotons made it the largest nuclear detonation up to that time , but it was considered inefficient and wasteful of the fissile material . Zebra , the third test , and the last of the Sandstone series , was detonated on Runit just before sunrise at 06 : 04 on 15 May 1948 . This test was characterized by AEC Chairman David Lilienthal as the " hardest and most important " test of the three . By using one of the B - class initiators , it demonstrated that these could still be used with confidence . The observers perceived the flash and blast as similar to the previous two tests , but this time the base of the condensation cloud was at , which gave the observers an unobstructed view of the fireball , which therefore appeared to be brighter and last longer than the other two . Looks were deceiving : its levitated uranium - 235 core produced a yield of 18 kilotons . The procedures used in the previous tests were repeated , but this time the winch cable snagged , and the test samples had to be retrieved by a jeep , exposing its crew to more radiation . The Los Alamos personnel assigned to remove the filters from the B - 17 drones had apparently carried out the procedure on X - Ray and Yoke without problems , but this time three of them suffered radiation burns on their hands serious enough to be hospitalized and need skin grafting . One of the men who had carried out the procedure for Yoke was then also found to have burns on his hands and was hospitalized too , but was discharged on 28 May . Once again the drone tank gave trouble , and bogged in the crater , but the soil samples were retrieved by the backup drone tank . Both tanks were subsequently dumped in the ocean . Outcome . The successful testing of the new cores in the Sandstone tests had a profound effect . Practically every component of the old weapons was rendered obsolete . Even before the third test had been carried out , Bradbury had halted production of the old cores , and ordered that all effort was to be concentrated on the Mark 4 nuclear bomb , which would become the first mass - produced nuclear weapon . The more efficient use of fissionable material would increase the nuclear stockpile from 56 bombs in June 1948 to 169 in June 1949 . The Mark III bombs were withdrawn from service in 1950 . At the same time , new production plants were coming online and the Wigner effect problem had been solved . By May 1951 , plutonium production was twelve times that of 1947 , while uranium - 235 production had increased eight - fold . The Chief of the Armed Forces Special Weapons Project , Major General Kenneth D . Nichols , saw clearly that the era of scarcity was over . He now " recommended that we should be thinking in terms of thousands of weapons rather than hundreds . "