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The first shot of Redwing, Lacrosse, was a test of a thermonuclear mockup for the TX-39 warhead (a redesign of the Mk-15). An externally initiated boosted primary was used in the device which was 34.5 inches in diameter, 100 inches long and weighed 8386 lb. The same primary was used in the Apache shot, conducted on July 9, 1956. This device primary stage was similar to the Mk-15/39 boosted primary which was later tested at the Nevada Test Site during Plumbbob Priscilla. Blast effects studies were conducted on jeeps and other vehicles during Lacrosse. 10 jeeps were placed facing into and broadside to the detonation at distances ranging from 2500 to 4380 feet from the shot cab. These were continuations of statistical studies from Operations Upshot-Knothole, Castle, and Teapot. Also shockwave precursor movement over vegetated earth surface versus sandy surfaces was examined. Lacrosse was fired at 06:25 on May 5, 1956 with a yield of 40 kilotons. The cloud reached an altitude of 35,000 feet, low for similar shots. The cloud had a pronounced brown hue to it. Cloud sampling aircraft penetrated the cloud 1.5 hours after the explosion. A crater 400 feet wide and 55 feet deep was produced. The northern set of islands received doses ranging from 9 to 10 R/hr gamma radiation four hours after the shot. The contamination of all the islands north of Runit resulted with the camps on Lojwa and Dridrilbwji being permanently closed. Road scrappers and bulldozers helped clean some of the islands following the shot by scrapping away contaminated soil and debris. |
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Cherokee, the second Redwing event, was the first U.S. airdrop of a thermonuclear device. Sponsored by the DOD, a LASL TX-15-X1 prototype device was tested, similar to the Zombie device tested during Operation Castle (Nectar) in 1954. The device was later developed into the Mk-15 bomb. Even though Operation Redwing was primarily a weapons development operation, Cherokee was a weapons effects test since it was the only air burst of a multi-megaton device tested by the United States to date. There were eight weapons effects programs, consisting of 47 projects, which were carried out by 18 different government agencies and laboratories. These programs centered on the Cherokee shot, which was used for military effects and fall out studies. Cherokee was also the first opportunity for the air force to test delivery of a high-yield thermonuclear weapon. The structure effects effort was concerned with checking the structure response to a multi-megaton blast. This was a continuation study from Operation Teapot, conducted at the Nevada Test Site. While structures were used during Teapot to measure effects from low yield bursts, Redwing allowed the same effects studies from high yield bursts. Cherokee was selected for this test. Six steel framed buildings were constructed on three manmade islands on the shallow reef between Charlie and Dog islands, and on the island of Dog. They were positioned at ranges of 20,500 feet, 24,000 feet, 29,000 feet, and 35,600 feet from the intended zero point. They were instrumented to obtain structural deflections, strains, and accelerations, as well as over pressure versus time and dynamic pressure versus time relationships. Another study was the movement of the shockwave through free-air. This was measured by a series of canisters dropped just prior to the explosion suspended by parachute. The canister drops were high coordinated to ensure data could be collected at different distances from the zero point. The Cherokee device was dropped from a B-52 over Bikini atoll and exploded at an altitude of 5,000 feet. It missed its intended target by over 4 miles to the Northeast of Namu Island. The Cherokee cloud reached an altitude of 94,000 feet. The bombing crew mistook a facility on another island as the targeting beacon. Virtually all military effects data was lost as a result of the bombing error. All of the blast effects structures that were located on the manmade islands were destroyed. The free-air canister study was only partially successful. The USS Mount McKinley was used as an observer ship for the Cherokee event. The Special Observer group was made up of 16 members of the press and news media, 17 civilian state and federal defense administrators, and 20 members of the Joint Office of Test Information. 38 aircraft participated in the test, including effects aircraft that were used to study damage caused by blast. This was done to gather data on the appropriate distance and timing needed for various aircraft to drop multi-megaton weapons. Effects aircraft that were used were an A3D-1, B-47, B-52, B-66, and F-84F. Cherokee was as much a political event as it was a practical test. Pressure caused by the Soviet Union’s successful air drop of a two-stage thermonuclear device (RDS-37, 1955), prompted the United States to follow suit. |
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The third Redwing shot, Zuni, was also the first test of a three-stage thermonuclear device. The University of California Radiation Laboratory (UCRL) device, called the Bassoon, was configured in its ‘clean’ version for the test. A lead tamper surrounded the third thermonuclear stage. The device weighed 12,158 lb and was later deployed in the Mk-41 bomb. The firing bunker on Eneu Island was evacuated for this test. Zuni was the only shot that required the evacuation of the entire atoll. The firing sequence thus was initiated from the USS Curtiss. Zuni was 1 of 3 surface shots during Redwing. The shot cab was located close to the 1954 Castle Koon zero point. Zuni was detonated at 5:56 local time with a yield of 3.5 megatons. The cloud reached an altitude of 85,000 feet and partially moved north at a speed of 15 knots. Later in the day the winds shifted to the south-east causing light fall-out on atolls southeast of Bikini. The resulting wind shift resulted in the contamination of a Japanese fishing ship 150 miles southeast of Bikini, the Mizuo Maru. Similar to the contamination of the Lucky Dragon during Castle Bravo, the Japanese fishing crew received high doses of radiation and suffered from acute shortage of white blood corpuscles. Bikini Atoll was highly contaminated following the shot. 75/R was measured at Bokbota and rates of 50/R was measured throughout the northern rim of the atoll. Eneu was only lightly touched by radiation. Reentry into Bikini atoll to collect instruments and samples began at H-hour + 2. Cloud sampling air craft penetrated the cloud less than 1 hour after the explosion. A crater 2,330 feet in diameter and 113 feet deep was created. The western end of Eneman Island was destroyed and the vaporized earth was pulled up into the fireball. Some of the debris that was pulled up into the cloud was residue left over from the Koon shot, which was considered a failure as the secondary stage failed to fire. The device was a success. 85% of the 3.5 megaton yield came from fusion. A ‘dirty’ version of this device, called Bassoon Prime, was later tested during Redwing Tewa. The MK-41 bomb this test helped to develop was later stockpiled from 1960 to 1976 and had a nominal yield of 25 megatons, the largest U.S. nuclear weapon ever stockpiled. |
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Yuma was a proof test of a linear implosion design intended for an air defense warhead. The device, known as Swift, was designed and developed by the UCRL. It had a diameter of 5 inches, length of 24.5 inches, and weighed 95 lbs. It was the smallest and lightest nuclear device tested to date. All islands except Parry, Ananij, and Enewetok were evacuated for the test.
At 07:56 on May 28, 1956, just one hour after the Zuni event, Yuma was fired atop its 205 foot tower. This was the first instance of near simultaneous detonations on both atolls. The test was a fizzle. The secondary stage failed to fire and the resulting yield (just 0.19 kilotons) was far below predicted estimates. The device used Octol 76/24 as the explosive trigger for the primary and had a plutonium core.
The cloud reached an altitude of 10,000 feet, the base reached 5,000 feet. It moved to the northeast at 10 knots. Eleven aircraft, including four F-84G cloud samplers, participated in the shot. Reentry commenced 1.5 hours after the shot. 3.3 R/hr was measured at Runit fours hours after the test, this was probably due from residue left over from Lacrosse being injected into the Yuma explosion.
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Erie was a test of a prototype of the primary stage from the Mk-28 thermonuclear warhead. The Mk-28 was stockpiled from 1958 – 1991 and had a nominal yield of 1.45 megatons. The test device was designed by the LASL and detonated atop a tower on Runit island. It was 20 inches in diameter, 55 inches long, and weighed 2106 lb. The test was conducted at 06:15 on May 31, 1956 with a yield of 14.9 kilotons. The cloud reached an altitude of 32,000 feet in about 10 minutes. Strong winds distorted the cloud but its red color helped identify it for cloud sampling missions. Only Runit was highly contaminated following the test. The southern end of the island was bulldozed to bring radiation levels to acceptable levels. |
A shot of particular interest during Operation Redwing was Seminole. It was a combined weapon development/effects test. The device was housed inside a large tank of water. Access to the device was through a small corridor, which was 10 feet off center inside the chamber. This factor produced an irregularly shaped crater. A TX-28 system was tested in Seminole with a primary fission stage of a Mk-28 bomb. The device was 20 inches in diameter, 55 inches long, and weighed 1832 lb. Cratering under controlled conditions was studied, as the purpose of the water tank was the simulate an underground burst. The tank was designed to couple the shockwave of the blast with the ground. The cloud from the explosion rose to an altitude of 16,000 feet, not mushroom developed. 45 minutes after the explosion the cloud separated into three parts. A crater 47 feet deep and 660 feet wide was produced. Eight aircraft participated in cloud penetration activities. Radiation was very high on the islands of Boken and Dridrilbwji, recovery operations on Dridrilbwji were delayed for two days. Helicopters visited the bunker on Boken on schedule. No cloud tracking missions were conducted because there was no above background off-atoll radiation detected. |
Flathead was a test of the TX-28S device, developed by the LASL. It was assembled at Parry Island at Enewetok Atoll and moved to Bikini onboard the USS Catamount with an escort destroyer. It was unloaded and moored on its barge to the zero point, 0.4 miles south of Iroij Island near the Castle Union crater. Flathead was detonated at 6:26 June 12, 1956. The cloud reached an altitude of 60,000 feet moving to the east at 15 knots. A B-57 penetrated the cloud 46 minutes after detonation. Flathead was a particularly ‘dirty’ device and heavily contaminated the atoll. 75% of the yield came from fission. Four hours after the test rated of 20-40 R/hr were detected at Bokbata and Lomilik. No radiation was detected at Eneu and recovery operations were not delayed. Radiation above background levels was detected at the atolls of Rongelap, Rongerik, Utirik, and Wake. The waters of the Bikini lagoon were highly contaminated. Eleven days after detonation radiation levels were still detected in the lagoon. The swimming beach on Eneu had to be closed as a result. |
This was a test of a small, light weight, low-yield air defense warhead. This was the first device to use plastic bonded explosive (PBX) for its implosion system. The diameter of the device was 11.5 inches and 23 inches long. The entire device weighed 130 lb, the nuclear component of the device weighed just 62.7 lb. Blackfoot was detonated atop its tower on Runit Island at 6:26 on June 12, 1956. It was detonated simultaneously with Flathead on Bikini atoll. Nine aircraft participated in the shot, none were effects aircraft. The cloud rose to an altitude of 30,000 feet and produced an anvil shaped mushroom. The cloud separated into three major components, it was reddish-brown in appearance making it very discernable for sampling pilots. The photographic tower on Unibor was heavily contaminated. This contamination interfered with later shots. |
Kickapoo was a UCRL device detonated atop a 300 foot tower on Aomon Island. The device, known as ‘Swallow’, was originally developed for an air defense warhead. The Swallow was 8 inches in diameter, and 28 inches long, and weighed 225 lb. It was the smallest and lightest device tested up until that time. It used Cyclotol 75/25 explosive for the primary stage and was plutonium fueled. Eleven aircraft participated in the shot. A F-101A effects aircraft was directly above the explosion at shot time. The supersonic aircraft outran the shockwave. The cloud topped off at 18,000 feet |
Osage was an airdrop test of a light weight LASL XW-25 warhead. It was dropped from a B-36 in an instrumented Mk-7 drop case that weighed 3150 lb. The device itself had a diameter of 17.4 inches, was 25.7 inches long and weighed 174.6 lb It detonated at 13:14 on June 17, 1956. It exploded 700 feet above Runit Island. DOD scientific experiments were all concerned with electromagnetic effects. 12 aircraft participated in the shot. The cloud reached and stabilized at 21,000 feet. Fallout was very little from Osage. |
Inca was a UCRL test of a multi-purpose tactical nuclear warhead. The prototype device was named the Swan. The device was later developed into the W-45 warhead. It was detonated atop its tower on Lujor at 9:26 on June 22, 1956. 12 aircraft participated in the shot, including three effects aircraft and six F-84G sampling aircraft. The cloud reached 42,000 feet, its stem moved west at 10 knots. The stem contained more debris then usual for similar yield shots. The shot island and lagoon were the only areas affected after the shot. Some fallout spread to Eleleron, the Mohawk shot island. |
This was a TX-28C variant prototype test. The LASL test device was 20 inches in diameter, 58 inches long, and weighed 1797 lb. The W-28 warhead this test helped developed became the most widely deployed design used by the United States. The warhead entered service in 1958 and remained in the stockpile until 1990. The last of the W-28 warheads was dismantled in 1991. It was deployed in 5 models with 20 different variants. Dakota was fired at 6:06 on June 26, 1956 5000 feet off Yurochi Island, over the Flathead crater. The cloud reached 81,000 feet. The upper portion moved west-northwest, middle cloud east-northeast, and bottom cloud stem northwest. The highest rate encountered by cloud sampling aircraft was 150 R/hr. The aircraft penetrated the cloud at 50,000 feet, planes at lower altitudes encountered considerably lower levels of radiation. Dakota exceeded its estimated yield by 25%. Several effects aircraft flying over the zero point at the time of detonation were considerably damaged by thermal and blast effects as a result of the higher then predicted yield. All aircraft returned safely. |
Mohawk, a UCRL device, was fired atop a 300 foot tower on Eleleron Island at 6:06 July 3, 1956. A boosted primary (Swan) and secondary (Flute) was used in the device which was 15 inches wide, 46.2 inches in diameter and weighed 1116 lb. The resulting crater from the explosion was 8 feet deep and 1340 feet in diameter. The cloud rose to an altitude of 65,000 feet. Cloudy conditions at Enewetok prevented atoll survey by P2V aircraft. 27 aircraft participated in the test, including 5 effects aircraft. 10 aircraft participated in cloud penetration activities. The shot heavily contaminated the shot island and strong radiation was detected on the north end of the atoll. Radioactivity was strong enough to fog the film of photographs taken by aircraft of the area two hours after detonation. Recovery operations were delayed for several days as a result of the high radiation levels on Eleleron. Changing wind direction to the south brought radioactive material to Parry Island two hours after detonation. Periodic showers contributed to light fallout on Parry Island, peak intensity being 0.002 R/hr. |
Apache was a test of a UCRL two-stage device using a ‘Zither’ secondary stage. It was a prototype for the Mk-27 warhead intended for the Regulus I missile. It was fired in the Regulus nose cone. A LASL primary design was used, which was tested earlier in Lacrosse. The test device was 30.2 inches in diameter, 69.8 inches long, and weighed 2941 lb. Apache was a barge shot fired in the Mike Crater on July 9, 1956. The cloud reached an altitude of 67,000 feet. 35 aircraft participated in the test, including eight effects aircraft. Apache produced high levels of fallout on the northern island and in the northern part of the lagoon. The swimming beach on Japtan was closed due to high lagoon radioactivity. Beaches were later closed on Parry and Enewetok. The Mk-27 was stockpiled from 1958 tp 1965. It had a nominal yield of 2 megatons. |
Navajo was the last LASL experimental device tested during Redwing. It was a test of the TX-21C thermonuclear device. It was detonated on a barge at 5:56 on July 11, 1956 near the Union crater, 0.4 kilometers south of Iroij island. The cloud stabilized at an altitude of 103,000 feet with a diameter of 140,000 feet. The lower and upper portions of the cloud moved west while the middle part moved east-northeast. 35 aircraft participated in the shot, 2 had to abort their missions however. Six early cloud penetration missions commenced 22 to 38 minutes after the detonation. Exposure rates of 60R/hr were recorded inside the cloud. Increased radioactivity was detected on Parry and Enewetok Island in the afternoon of shot day, but only lasted for two hours before levels dropped down to the previous reading. Wotho and Utirik were only lightly touched by radiation. Biomedical effects studies were done on animals during Navajo, as well as 10 other Redwing shots.. Protection against chorioretinal burns during the initial flash of light from a nuclear explosion was studied. Rabbits and monkeys were exposed to the thermal pulse of the explosion. Filters and lenses of different types were fixed over the eyes of the animals. The blink reflex is too slow to prevent chorioretinal damage observed during the initial thermal pulse. This data was essential in the development of eye protective devices. Another study done during Navajo was water waves created by the energy released from a multi-megaton explosion. Cameras 18 miles away on a beach on Namu Island recorded a wave 11 feet in height covering the island 17 minutes after detonation. Navajo was a very clean device, the cleanest U.S. device ever tested. 95% of the yield came from fusion, resulting in relatively low fallout considering the size of the explosion. The yield was within the predicted range. |
Tewa was the last shot at Bikini atoll during Operation Redwing. The UCRL ‘Bassoon Prime’ device was a dirty version of the Zuni device. It was a three-stage design, the first of its type developed by the United States. The device itself was 39 inches in diameter, 135.5 inches long, and weighed 15,735 lbs. The barge was located over the reef between the islands of Namu and Yurochi. Tewa was detonated at 5:46 on July 21, 1956 with a yield of 5 megatons, the largest Redwing event. The cloud reached an altitude of 90,000 feet, with the base at 30,000 feet. The cloud moved West toward Enewetok, except for the lower portion which moved east. A crater 4000 feet in diameter and 129 feet deep was created in the reef. 24 aircraft participated in the shot. Three aircraft were used for weapons effects experiments and eight were used for sampling missions. Early penetration sampling pilots received a maximum exposure of 3.1 R. Tewa heavily contaminated the northern islands of Bikini atoll. Every island except Eneu was contaminated by the blast. Recovery missions were delayed due to the high levels of radiation detected. A fall out incident was caused by Tewa after winds changed direction suddenly following the test. A small, unpredicted vortex appeared over Bikini at shot time at the 30,000-40,000 foot level. Winds pushed the radioactive cloud toward Enewetok atoll where personnel were exposed to fallout. Four aircraft monitored the cloud as it drifted toward Enewetok. Nine hours after detonating the fallout reached Enewetok atoll. Background radiation levels rose suddenly on Parry Island. Enewetok also detected fallout, however, no other islands were affected. Subsequent rain showers over Enewetok and Parry Islands worsened the fall out problem, which lasted for approximately 17 hours. Puddles of rainwater, especially on Enewetok parking lots and runway showed levels 10 times above the general area level. Three ships, the USS Curtiss, USS Ainsworth, and USS Knudson, were dispatched from Bikini to Enewetok incase evacuation of the atoll had to be conducted. All three ships encountered radioactive fallout on the way to Bikini atoll. The ships were buttoned down and wash-down commenced every 15 minutes. The first ship to enter the lagoon was the Curtiss followed by the Ainsworth and later the Knudson. Periodic rain showers throughout the fallout period continued at Enewetok. Personnel were requested to remain indoors for as long as possible. The rain showers helped wash off radioactive debris from roofs of buildings and other structures but also concentrated fallout in eaves of buildings. Initial estimate of exposures was 2.5 R. Later estimates indicated actual exposure rates between 3 to 6 R. After the fallout, a survey was made of Parry Island. Decontamination of hot spots on the atoll was initiated but little was accomplished until recovery operations for the following Huron shot were completed. Living quarters and the movie theater were decontaminated. Grading adjacent to barracks and offices reduced exposure rates by an average factor of three. At the outdoor theater, removal of seats and removal of the top layer of dirt, with subsequent backfilling with clean dirt, reduced gamma levels by a factor of ten. The fission yield of Tewa was 87% of the total yield, the highest known fission yield of any U.S. thermonuclear test. The lead tamper used during the Zuni test was replaced with a Uranium tamper, resulting in the high fission yield. The device was later developed into the Mk-41, the most powerful nuclear weapon developed by the United States. |
Huron was a test of the W-50 prototype, a LASL two-stage thermonuclear device. The device, called ‘Egg’, had a diameter of 15.3 inches, length of 43.1 inches, and weighed 793 lb. The last Redwing shot, it was fired on July 22, 1956 at 6:12 in the Mike crater. No ships were evacuated from Enewetok lagoon for the shot. 21 aircraft participated in the shot, including five effects aircraft. The shot heavily contaminated the northern islands of the atoll. Huron was fired when fallout from the Tewa shot, detonated just 24 hours earlier, was still covering the islands. Huron did not add to this fallout. The W-50 warhead was stockpiled from 1963 to 1991 and yielded 60 to 400 kilotons. It was used on the Pershing tactical surface-to-surface missile deployed in Europe. |
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