BACKGROUND.

When Operation Crossroads was conceived in 1945, there had been three nuclear explosions. Crossroads, consisting of two events. was designed primarily to provide information on atomic bomb effects on naval vessels. Nearly 100 ships and submarines were in the target fleet inside the Bikini Atoll. Types of naval vessels included battleships, aircraft carriers, destroyers, transports, submarines, dry docks, and landing craft. During the testing, several submarines were submerged and some of the landing craft were on the beach. The ships were ]loaded with fuel, ammunition, animals, food grains, and exposed Army combat equipment to simulate baffle conditions.

The nuclear devices used for Able and Baker were similar to those of Trinity and Nagasaki. The Able device was dropped by a B-29 aircraft and detonated at about a 500-foot altitude. The bombardier apparently missed the desired GZ by approximately 2,000 feet; the actual detonation point was never precisely determined. The Baker device, suspended from a landing ship, was detonated about 90 feet below the surface of the ocean.

There was considerable interest in attempting to quantify phenomena associated with a nuclear airblast Mach stem, and a number of rather primitive blast gauges were hurriedly created and fielded. Due to the uncertainty of the Able detonation point, no useful blast measurements ;were collected

In considering the types and quality of nuclear weapon effects data that are available from the Crossroads operation, two factors need to be considered:

1. Crossroads was actually the first nuclear weapon effects test series. Trinity was obscured in secrecy, and there was little chance to plan and implement weapon effects activities. The only other previous nuclear detonations were those at Hiroshima and Nagasaki, which had no instrumentation or technical observers. Hence, the experimenters approached Crossroads with no experience, resulting in relatively little data acquisition.

2. Since World War II had ended shortly before the Crossroads operations, a wealth of surplus war equipment was available for exposure to nuclear tests.

Crossroads experiments were in two programs. The first program was under the Director of Ship Material (DSM) and included the collection of information from the exposure of ships and equipment. The DSM program was in turn divided into groups that were oriented along the organizational lines of the interests of the services (primarily the Navy) and whose experiments reflected these interests. The largest group was that of the Navy Bureau of Ships (BuShips), which reported on each exposed ship for each test, summarized results by class of material (e.g., welding, yardarms, etc.) in a series of special reports, as well as summarizing results overall. BuShips Instrumentation [sub]Group reports attempt to measure airblast and other weapon phenomena.

The second experimental program was under the Technical Director. In this program. measurements of pertinence to weapon physics were made along with measurements pertinent to weapon effects.
 

Petroleum Products XRD-7

The objective of this project was to assess the effects of nuclear bursts on fuels and lubricants commonly used on ships. Army petroleum samples were also exposed. Tested materials included fuel oil, turbine lubricating oil, diesel fuel, and hydraulic oils taken from the target fleet. The samples were exposed to the burst in containers. XRD-7 indicates little or no change in petroleum product properties.

Special Reports on Hull Items XRD-8

Special nuclear weapon effects studies on submarine salvage fittings, flooding sources, turret structures, and protective paints were performe~ Evidence of problems and recommendations for solutions are presented.

Special Reports on Machinery Items XRD-9

Special nuclear weapon effects studies were performed on boilers, uptakes, and stacks, piping and fittings, deck machinery, main turbines and gears, and auxiliary machinery. Results and observations relevant to future naval vessel design are presented.

Special Reports on Electrical Items XRD-1O

Nuclear effects on a wide variety of shipboard electrical equipment are addressed. Equipment includes propulsion systems, motors, control systems, generators, batteries, and telephone systems. Effects data from the entire target fleet are assembled and assessed.
Oi'erall Summaries of Target Vessels
XRD-11, -12, -13, -14

Nuclear weapon effects on each vessel in the Able and Baker events are summarized. Specific recommendations relating to each vessel are made. Reports describing specific types of damage observed throughout the target fleet and two reports (one for Able and Baker) were submitted for each ship or set of ships exposed during the tests. The damage reports on the individual ships are numbered XRD-16 through XRD-148 and are not discussed flirther in this guide.

BuShips Instrumentation Group

Various measuring devices were placed on vessels by BuShips Instrumentation Group to record blast and shock phenomena during the detonations. Descriptions of the devices and the resulting measurements are given in the reports below.

Accelerometers, Reed Gauges and Seismic Instruments XRD-193

Instruments to measure accelerations and low-magnitude shocks were installed in vessels at various distances from GZ. The report describes the gauges, their location, and the resulting measurements.
 
 
 

Airbiast pressure measurements, both feee field and at selected locations on ships, were made during Able and Baker. Two ships carried diaphragm and piston gauges in each test. Raw data records and processed data are reported, along with descriptions of gauge operation and data analysis.
XRD-196
Strain and Displacement Measurements

Strain and displacement gauges were installed in ten ships and submarines. XRD-196 contains a complete listing of data, location of ships and gauges, and thorough posnest analyses. Readings were universally smaller than expected.
Velocity-Time Measurements XRD- 197

Thirty-two velocity meters were installed on selected structures of four exposed vessels. The vessels varied in distance to GZ. Able produced minimal data, since one instrumented ship sank and the other three were far from the detonation. Extensive data are reported for Baker, including raw data traces. Good posnest analyses were performed.
XRD-198
Impulse Velocity Gauge Measurements

A gauge for measuring peak velocities of shock-loaded structures was developed for use in Crossroads. The rigidly mounted diaphragm deformed in proportion to the impulse propelling the structure. Since the gauge was simple, inexpensive, and self-recording, many were mounted on structural elements of several target vessels. XRD-198 describes the gauge, its operation, location, and the implied velocity measurements.
Underwater Pressure Measurements-Ball Crusher XRD-199

A pressure-recording gauge based on the principal of ball deformation by a pressure-driven piston was used extensively in Crossroads. Gauges were deployed at various water depths near ships and on hulls. Underwater peak pressure measurements at a variety of locations from GZ are reported along with calibration curves to relate ball deformation to pressure.
Displacements of Shock-Mounted Equipment XRD-200

The objective of this project was to measure the maximum displacement of shock-mounted equipment at various locations on ships at various distances from the nuclear burst points. Lead gauges that deformed plastically were employed. The shock mounts are described and gauge readings are reported.
XRD-201
Shock Measurements

The report describes measurements and data plots of shock-induced motions of ships. A variety of pressure, velocity, and displacement gauges were mounted aboard 25 vessels to determine the forces to which shipboard equipments are subjected.
 
 

Icaroscopes XRD-202

Devices capable of presenting images of the fireball with low enough intensity for direct viewing without filtration were attached to cameras as well as for direct viewing by participants. Two such cameras obtained succesful pictures on Able and fire ball diameters were determined and recorded in XRD-202.

Roll and PUck Measurement XRD-203

Gyroscopes and pendulum recorders were installed on 13 target ships to measure the roll and pitch of vessels exposed to nuclear bursts. The report consists of general observations and recorded data.

Measurements of Peak Pressure and Vacuum XRD-204

The objective of this project was to measure positive and negative pressures external to the ships and at various locations inside ships exposed to nuclear bursts, The report contains a significant number of pressure gauge readings, but the measuring technique is questionable.
Army Group XRD-149

The document is a summary of Army activities during Operation Crossroads. Experimental details appear in reports XRD-15O through XRD-156 which follow.

Engineer XRD-15O

The objective of this project was to assess nuclear weapon effects on standard Corps of Engineers equipment. Test hardware included construction equipment, floating bridges, water supply equipment, mine detectors, and batdefield equipment. Photographs of test items and comments on survivability are presented.

Signal XRD-1S1

XRD-15l contains detailed descrintions of hardware and test results. The objective of this project was to evaluate nuclear weapon effects on Signal Corps communication equipment. Experiments were passive, and assessments vere made on the operability and repairability of the equipment after exposure. A complete listing of test hardware and the experiment locations is provided. along with pretest and posttest operations.

Ordnance XRD-152

A number of Army tanks, guns, and artillery pieces, and ammunition were deployed on the decks of ships in Operation Crossroads. The effects from Able were more significant than those from Baker. It was generally concluded that personnel manning the ordhance were more vulnerable than the equipment. Several good, but general, observations are reported in XRD-152, along with detailed descriptions of hardware and response.

Chemical XRD-153

The objective of this project was to assess the response of chemical warfare equipment to a nuclear weapon environment. Chemical weapon containers, detoxification materials, and protective clothing were exposed in the Able event at six different test stations on ships. Descriptions of test hardware and response to the nuclear environment are described.
 
 

The objective of this project was to determine the response of standard Quartermaster supplies, including subsistence, clothing, individual equipment, and repellents, to nuclear environments. Deployment included normal usage and storage conditions. Descriptions of test items, test positions, and posttest conditions, including photographs. are presented.

Air XRD-156

BuAer exposed 73 Navy aircraft to the Crossroads nuclear environments. These included observation planes, carrier combat planes, and moored seaplanes. The aircraft were deployed on warships and transports in normal wartime disposition. A few bad fuel and ammunition. Airplane damage after each nuclear testis described and numerous photographs are provided.
Bureau of Ordnance (BuOrd) Group Final Report XRD-158

The BuOrd objective was to assess the capability of naval ordnance systems and equipment to operate in nuclear environments. Test hardware was fielded on 14 ships. Guns, mounts, torpedoes, and fre~ontrol systems were evaluated before and after exposure. Observed effects are summarized.
XRD-159
Fire Control

The objective of this project was to evaluate the response of fire-control optics and fire-control radar to nuclear detonations. Surface ship and submarine systems were tested. Pressure gauges and accelerometers were installed at certain ordnance locations. Several systems were energized before exposure. Postexposure condition of numerous systems is reponed.

Photographic Appendix XRD-160

Naval guns and gun mounts were exposed at various ranges from the Crossroads nuclear detonations. Equipment damage is described with supporting photography.

Armor and Metallurgy XRD-162

Bureau of Medicine and Surgery (BuMed) Group Report,
XRD-163
Sample Locations

A large number of biological specimens were exposed on ships to study the biological effects of nuclear environments. Items tested included goats, pigs, rats, soils, microorganisms, plant seeds, biological warfare agents, and radiation dosimeters. XRD-163 identifies the test location of each
 

Airbiast Effects of An Atomic Bomb Explosion XRD-164

Gross Autopsy Findings and a Statistical Study of the Mortality in the Animals Exposed at Bikini
XRD-165
The project recorded the survival period of each of the animals exposed in Crossroads at various ranges and shipboard locations. Data tables and plots of animal mortality as a ninction of time and distance from detonation are presente~

Germination of Vegetable Seeds Exposed at Bikini

During the Atomic Bomb Test Able XRD-170

Residual Effects of Atomic Radiation in Soil on

Seed Germination XRD-171

Effect of the Bikini Atomic Bomb Test Able

on Soa Microorganisms XRD-172

Analysis of Tissues for Induced Radioactivity XRD-175

Vycor Glass Gamma Ray Dosimeters XRD-176

Second-generation seeds from those exposed in Crossroads were planted and the resulting plants analyzect
Electronics Coordinating Officer Reports XRD-180, -181

This project provided extensive tabular and photographic coverage of damage to antennas and electronic elements, including vacuum tubes, cables, mountings, waveguides, sonar, Army Signal Corps equipment and plastics and paint
Bureau of Yards and Docks Group Final Report XRD- 182
The objective of this project was to measure the effects of nuclear explosions on three concrete boats in order to be able to assess the potential effects on land-based concrete structures. Concrete test hardware included a 2,800-ton dry dock, a gasoline barge, and a fuel oil barge. The damage sustained during Able and Baker is described, with comments on the implications.
Bureau of Supplies and Accounts Group Final Report XRD-183

Effects of a nuclear burst on food (fresh, frozen, dried) and clothing stored in normal locations on four target ships are described.
Maritime Commission Representatives Final Report XRD-184

General observations are made assessing damage to ships built by the Maritime Commission and new fabrication techniques to enhance ship survivability are identifici

Radiological Decontamination of Vessels
XRD-185, -186, -187

Vessels in the target fleet and ships supporting Crossroads had to undergo a decontamination process. XRD-185, -186, and -187 describe experimental techniques employed and the degree of success achieved.
 

This program covered such nonmeasurement areas as weapon preparation and radiological safety but also had groups making measurements of blast, wave motions, EM propagation, and thermal and optical radiation via remote measurement techniques and technical photography. In the blast area, the intent was to take measurements in free air, whereas the BuShips Instrumentation Group (above) was to take measurements "in and around" the target ships. However, it appears that there is much overlap between the instrumentation indexed in Appendix N of the Technical Directors Reports (XRD-209, -210) and that discussed in the BuShips Instuumentation Group reports
(XRD-192 through XRD-204). XRD-209, -210
 

The objective of this project was to provide a detailed description of the BUcini Atoll as it existed before and after the nuclear tests. XRD-212 contains detailed descriptions of sunken vessels and