Operation Ranger

Operation Ranger - 1951

Operation Ranger was the first nuclear testing series conducted at the Nevada Test Site, then called the Nevada Proving Grounds. Sponsored by the Atomic Energy Commission (AEC), Ranger was conducted between January 25 to February 6, 1951. The series featured five nuclear detonations and a single, high explosives test fired on January 25, 1951 to calibrate equipment for the upcoming nuclear tests. The series was intended to provide data for use in determining design criteria for nuclear devices scheduled for detonation at Operation Greenhouse, to be conducted at the Pacific Proving Grounds from April 7 to May 24, 1951. Ranger saved the weapons development program months of time and helped test the concept of small, atomic weapons.

Fox explosion
(February 6, 1951)

In November 1950, the Los Alamos Scientific Laboratory discovered that insufficient data were available to determine satisfactory design criteria for nuclear devices to be tested in Operation Greenhouse. The LASL scientists believed that variations in the compression of the critical material could affect the yields of the Greenhouse devices. To confirm this hypothesis, LASL held conferences on December 6 and 11, 1950 and concluded that a series of small nuclear tests should be conducted to improve the Greenhouse design criteria. On December 22, 1950, LASL requested approval for a continental series from the AEC Division of Military Application (DMA). DMA approved the request and asked for Presidential approval to expend the fissionable material required for the series. The White House responded affirmatively on January 11, 1951, formally creating Operation Ranger.

The same day that Operation Ranger was approved by the President, the AEC distributed its only announcements of the series. Handbills were circulated in the area of the NTS stating that from January 11, 1951 nuclear tests would be conducted at Las Vegas Bombing and Gunnery Range.

Operation Ranger was the first time nuclear devices were detonated within the continental United States since the Trinity test in 1945. The series was hastily arranged and a relatively small series compared to subsequent operations at the NTS. 360 Department of Defense personnel participated in air support services, scientific experiments, weather support, communications security and observer programs. Since Ranger was only a 13-day operation, the same units and participants performed the same duties throughout the series.

Construction at Frenchman Flat prior to Operation Ranger

The Nevada Test Site was divided into two geographical areas: Yucca Flat and Frenchman Flat. Yucca Flat, located in the north-central part of the NTS, is a 192-square-mile desert valley surrounded by mountains. This area was the location of many nuclear detonations after Operation Ranger. Frenchman Flat, which includes a 9-square-mile dry lake, is located in the southeastern part of the NTS.

The Ranger Control Point, which served as AEC operational headquarters, was 8 miles south of ground zero. It was a hastily constructed building that included a control room, administrative office, first-aid station, and shower for personnel decontamination. Two photography stations were located near ground zero. One station was 2 miles to the southeast on the dry lake. The lake bed also served as the Frenchman Flat landing strip because of its smooth, hard surface. The other station was 2 miles northeast of ground zero. Extending from ground zero to the west was the West Access Road, north of which lay the field fortifications area, used extensively in scientific experiments.

The majority of the DoD participants performed air support services provided by the Air Support Section of the Test Group. Air Force personnel from the Special Weapons Command (SWC), and Headquarters, United States Air Force, conducted most of these activities. For each shot, air support activities included the airdrop of the nuclear device, cloud sampling, cloud tracking, aerial surveys of the terrain, meteorological services, communications security, courier service, and monitored worldwide radioactivity from the Ranger tests for the Atomic Energy Detection System.

Control Point 8 miles south of Ground Zero

The Scientific Tests Section of the Test Group administered projects at each nuclear detonation. DoD personnel were involved in eight projects at each test except for the Baker shot, where they took part in seven experiments. Of the 12 known DoD participants, six were from the Army Participation Group, an organization representing the Chief, Armed Forces Special Weapons Project. The other six were officers from the Army, Navy, and Air Force. Participants in these scientific experiments placed film badges, fabrics, and other materials and instruments in or around military fortifications constructed in the ground zero area. They retrieved the equipment after the detonation, when radiation levels had decreased and limited access into the shot area was permitted.

Primary Army participation came from the 82nd Reconnaissance Battalion from Fort Hood, Texas, which provided security at the test site. The number of observers at Ranger has been documented as 156, but only three of these are believed to have been military personnel.

All five nuclear devices were dropped from B-50 bombers over Frenchman Flat from a height of 19,700 feet above the ground with the exception of the Fox shot, which was airdropped from a height of 29,700 feet. The first four devices were modified Mk-4 weapons, designed to test different design parameters for yield. The last shot, Fox, was a test of the new Mk-6 weapon and proof tested the Fox composite core. All of the nuclear devices weighed 10,800 lb and had 60 inch diameters. The high explosive assembly, core, and firing system of each device weighed 7,100 lb.

The Tests

Code Name: Able
Time and Date: 5:45 January 27, 1951 (local)
Location: Frenchman Flat, Nevada Test Site (NTS)
Height: 1060 feet
Type: Air Burst - Air Drop
Predicted Yield: 1.3 kt
Actual Yield: 1 kt

Able, the first test of Operation Ranger, was a compression vs. critical mass test using an all-oralloy core. The device used a type D pit in a Mk 4 high explosive assembly.
At shot-time, the temperature at the surface was -2.0 degrees Celsius, and the winds at the surface were nearly calm. At 10,000 feet, winds were 18 knots fromt he west, and at 20,000 feet, winds were 30 knots from the west. The top of the nuclear cloud reached an altitude of 17,000 feet and moved east from the point of detonation.
The initial ground survey found that on site radiation greater than 0.03 R/h was confined to an area 1,472 meters from ground zero, reaching a maximum intensity of 0.75 R/h near ground zero. Intensities exceeding background radiation were detected 10,240 feet from ground zero.
A B-50 aircraft delivered the Able nuclear device. Two other aircraft, a B-50 and a C-47, accompanied the drop aircraft for the purpose of documentary photography and emergency assistance, respectively.
The B-50 drop aircraft, with a crew of 11 from the 4925th Special Weapons Group, left Kirtland Air Force Base at 0115 hours on shot day and flew at an altitude of 14,000 feet to Indian Springs AFB. Upon reaching the Indian Springs area, the aircraft descended to 10,000 feet and proceeded to the north of ground zero. At 0350 hours, the crew began inserting the nuclear capsule into the device, completing this task at 0434. The aircraft then climbed to its bombing height of 19,700 feet. It completed its first practice run at 0507 and its second practice run at 0520. At 0527, the bomb-bay doors were opened, and at 0534, the B-50 began its bombing run. At exactly 0544:05 hours, the device was released. The B-50 then returned to Kirtland AFB, arriving at 0750 hours
The main objective of the DoD was to collect data on the effects of gamma and thermal radiation from a nuclear detonation. The Scientific Tests Section, part of the AEC Test Group, fielded eight experiments at Able. Twelve DoD participants took part in these experiments. An estimated 246 Air Force personnel engaged in air support.

Code Name: Baker-1
Time and Date: 5:52 January 28, 1951 (local)
Location: Frenchman Flat, Nevada Test Site (NTS)
Height: 1080 feet
Type: Air Burst - Air Drop
Predicted Yield: 9 kt
Actual Yield: 8 kt

Baker-1 was detonated on January 28, 1951 at 5:52 local time 1,080 feet over Frenchman Flat. At shot-time, the temperature at the surface was -2.8' C, the relative humidity was 87 percent, and the atmospheric pressure was 13.04 psi. The winds were six knots from the south-southwest at the surface, 13 knots from the west at 10,000 feet, and 33 knots from the west-northwest at 30,000 feet.
Analysis of Fireball Growth was conducted by LASL. The objective was to analyze the fireball growth and yield determination by studying film from cameras at photography stations 2 miles southeast and northeast of ground zero. A special LASL group, consisting of three civilian employees and one Army, one Navy, and one Air Force participant, retrieved film from the photography stations after the test and returned it to LASL for analysis.
Soon after the detonation, on site induced activity greater than 0.3 R/h was confined to an area 460 meters from ground zero; intensities climbed to 16.0 R/h within 90 meters of ground zero. Lighter activity, ranging from 0.0001 R/h to 0.3 R/h, was confined to an area 3,200 to 460 meters from ground zero.
The B-50 drop aircraft, with a crew of 11 from the 4925th Special Weapons Group, left Kirtland AFB at 0105 hours on shot day and flew at an altitude of 14,000 feet to Indian Springs AFB. Upon reaching the Indian Springs area, the aircraft descended to 10,000 feet and proceeded to the north of ground zero. At 0342, the crew began inserting the nuclear capsule into the device, completing this task at 0418. The aircraft then climbed to its bombing height of 19,700 feet. It completed its first practice run at 0447, its second practice run at 0508, and its third run at 0525 hours. At 0530, the bomb-bay doors were opened, and at 0538, the B-50 began its bombing run. At exactly 0552:l0 hours, the device was released. The B-50 then returned to Kirtland AFB, arriving at 0751 hours.
Baker-1 was a "fractional crit" test. A core with less than one critical mass of material, at normal density, was imploded to super-criticality by high implosion pressure. The device used a type D pit and was used in a Mk 4 high explosive assembly. Was the first use of the TOM initiator.

Code Name: Easy
Time and Date: 5:47 February 1, 1951 (local)
Location: Frenchman Flat, Nevada Test Site (NTS)
Height: 1080 feet
Type: Air Burst - Air Drop
Predicted Yield: 0.6 kt
Actual Yield: 1 kt

At shot-time for the Easy test, the temperature at the surface was -11.5' C, the relative humidity was 89 percent, and the atmospheric pressure was 13.33 psi. The wind was two knots from the north at the surface and at the height of burst, increasing to ten knots from the north-northeast at 5,000 feet, 26 knots from the north-northwest at 10,000 feet, and 39 knots from the north-northwest at 12,500 feet.
The B-50 drop aircraft, with a crew of 11 from the 4925th Special Weapons Group, left Kirtland AFB at 0116 hours on shot day and flew at an altitude of 14,000 feet to Indian Springs AFB. Upon reaching the Indian Springs area, the aircraft descended to 10,000 feet and proceeded to the north of ground zero. At 0357, the crew began inserting the nuclear capsule into the device, completing this task at 0430. The aircraft then climbed to its bombing height of 19,700 feet for two practice runs. At 0515,the B-50 began its bombing run. At exactly 0546:02 hours, the device was released. The B-50 then returned to Kirtland AFB, arriving at 0751
Easy exploded at 5:47 on February 1, 1951 (local). This was another compression vs critical mass test to obtain a different point on the compression vs yield curve. Easy used a type D pit in a Mk 4 high explosive assembly.
One hour after the detonation, on site induced activity greater than 0.01 R/h was confined to an area 500 meters from ground zero. A maximum radiation intensity of 0.55 R/h was detected at ground zero. Radiation readings of 0.005 R/h were measured 2,880 feet from ground zero.

Code Name: Baker-2
Time and Date: 5:49 February 2, 1951 (local)
Location: Frenchman Flat, Nevada Test Site (NTS)
Height: 1100 feet
Type: Air Burst - Air Drop
Predicted Yield: 9 kt
Actual Yield: 8 kt

At shot-time, the temperature at the surface was -9.2' C , the relative humidity was 79 percent, and the atmospheric pressure was 12.8 psi. The surface winds were calm. Winds were 22 knots from the west-southwest at 10,000 feet and 45 knots from the northwest at 20,000 feet .
The Baker-2 was a test of the reproducibility of weapons performance and was identical to the Baker-1 device. It was detonated at 5:49 on February 2, 1951 over Frenchman Flat.
About one hour after the detonation, onsite induced activity greater than 0.5 R/h was confined to an area 450 meters from ground zero. Lesser intensities, ranging from 0.5 R/h to 0.0004 R/h, were confined to an area 2,880 feet to 11,520 feet from ground zero.

Code Name: Fox
Time and Date: 5:47 February 6, 1951 (local)
Location: Frenchman Flat, Nevada Test Site (NTS)
Height: 1435 feet
Type: Air Burst - Air Drop
Predicted Yield: 34 kt
Actual Yield: 22 kt

Fox was the last and largest Ranger shot. Detonated on February 6, 1951 at 5:47, it proof tested the FOX composite core using a Type D pit and was dropped in a Mk-6 bomb, which used the HOW double prime high explosive assembly. The test device was nick-named "Freddy".
At shot time, the temperature at the surface was -2.0 C, the relative humidity was 85 percent, the atmospheric pressure was 13.2 psi. Surface winds were light and variable one hour and 45 minutes before the shot. Winds were 27 knots from the northwest at 10,000 feet and 45 knots from the west-northwest at 30,000 feet.
One hour after the detonation, on site induced activity greater than 0.16 R/h was confined to an area 2,880 feet from ground zero. The maximum radiation intensity, 15.5 R/h, was detected at ground zero.

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