Defense against nuclear weapons at sea has had a profound influence on modern naval thought and operations. These new weapons have not meant the end of sea power, as many once predicted they would, but they have dictated many departures from standard naval doctrine. Yet, while doctrine changed to adapt to the new threat, some time-proven, basic military countermeasures—proper preparation, training, and tactical skill—have survived the crucible of nuclear testing and are as important today as ever to naval forces.
For centuries, naval commanders have had to deal with tangible, easily understandable dangers. Today, the force commander must also cope with the silent, invisible effects of ionizing radiation released in a nuclear explosion.
An interesting parallel can be drawn between decisions and risks at sea today, and a well-known example of calculated risk in World War II. In December 1939, Commodore Henry Harwood, Royal Navy, pitted his three-cruiser squadron against the German pocket battleship Graf Spee even though the German ship’s batteries outranged his, and exceeded in broadside weight the combined total of all three British cruisers. In spite of these imposing odds, Harwood defeated the Graf Spee in an action that was remarkable for its display of dogged determination and superior tactical handling of the cruisers.
Today, a commander can be equally skillful and successful in the face of nuclear attack. Instead of consulting range and armor penetration tables, or using smoke screens as Harwood did, he will consider such factors as pre-attack dispersion, evasive maneuvers, gas- tight envelope, washdown, deep shelter, radiation exposure, and decontamination. He may, however, have to take the calculated risk of exposing his personnel to ionizing radiation. How well he survives this attack will depend on his prior preparation, the readiness and state of training of his ships, the measures he takes to minimize ship damage and personnel casualties, and his post-attack maneuvers and countermeasures.
Admittedly, there is an element of chance against which no amount of training and knowledge can prevail. History is replete with examples of ships sinking immediately from a single salvo or a lone torpedo hit. Today, any ship unfortunate enough to be at surface zero of a nuclear weapon burst, except a high altitude burst, undoubtedly would be destroyed. In a widely dispersed force, however, very few ships would be in the absolute lethal area. Tests have shown that the others can survive—and survival with minimum damage is the primary objective of defense against nuclear attack.
Of the many considerations for defending a ship against nuclear weapons effects, the primary one is: “How close is surface zero?” Next comes, “What type of burst is it?” These two questions eliminate numerous other variables and narrow the problem.
A ship close to zero must contend with air blast, underwater shock, thermal radiation and initial ionizing radiation. A ship at some distance from zero is primarily concerned with residual transit and deposit radiation. The effects of blast, shock, light, and heat can be seen and felt immediately, but the effects of transit and deposit radiation occur later and their presence can be detected only with instruments.
For a given yield, greater ship and equipment damage are produced by an underwater burst. The cause of the damage is an underwater shock wave which initially travels at several times the speed of sound, but quickly slows to sonic speed in water (5,000 feet-per- second). Shock can rupture hulls and derange equipment and machinery. The underwater shock-force is mechanically transmitted throughout the ship’s structure in a way that produces a rapid displacement upward. Unless personnel stand with their knees flexed and hold on to some solid part of the ship’s structure, they are likely to be “hit” by the deck, or thrown into the overhead or bulkheads in such the same manner as from mine explosions in World War II. The primary defense against underwater burst is conventional damage control.
The effects of air blast, thermal radiation, and initial ionizing radiation are the primary immediate dangers to ships close to the fireball of a surface or air burst. Air blast creates a high wind which can bend or drag topside fixtures and throw exposed personnel about. It also causes a high static overpressure which tends to squeeze and crush targets. Thermal radiation is the heat and light from the fireball; it travels at the speed of light and arrives before the shock of the air blast. It does not present a significant fire hazard to the ship’s structure, but it will harm exposed topside personnel, causing skin burns, flash blindness, and retinal burns. Initial ionizing radiation consists essentially of neutrons and gamma rays emitted by the fireball and the mushroom cloud during the first minute after detonation. This radiation does not cause appreciable material damage, but it will produce “combat ineffectives” among the crew.
Personnel defense against the effects of surface and air bursts is time phased. At the first flash, exposed personnel should close their eyes, cover their faces with their hands, and drop to the deck behind the best shelter available. After the flash or heat sensation is over, they should then grasp some part of the ship’s structure before the air blast hits.
The defense against ionizing radiation is to seek cover. With adequate warning, many personnel normally stationed topside can go below to “deep shelter” below the waterline, otherwise, at detonation, the shelter available to anyone topside is chancy, depending on the amount of shielding material between the man and the source of radiation. The fallout hazard may persist up to 24 hours, depending on weapon yield and burst conditions.
For the majority of ships defending against nuclear weapons—regardless of their proximity to surface zero—the most important element of consideration will be radioactive fallout. This type of contamination is like rain, but it can be either dry or wet, it be either visible or invisible, and it can spread over large areas. It consists of very small radioactive dirt, dust or water particles which adhere tenaciously to dry surfaces and emit deadly radiation.
Because earlier tests had shown that water can decontaminate surfaces that had been subjected to radioactive fallout, U. S. Navy ships participating in the March 1954 Pacific test had been equipped with a “washdown system” capable of covering topside areas with a spray of clean sea water. Ten ships 25 miles from the explosion were unexpectedly subjected to fallout. By energizing the washdown system and sending most personnel below decks, the ships survived the danger of fallout, and no one on board received excessive radiation.
The initial installation of washdown systems throughout the Fleet was accomplished by ship’s force. The “interim” system, consisting of spray nozzles, plastic piping, and portable manifolds, needed fire hose connections from topside fireplugs. Each nozzle produced a circular pattern of spray about 20 feet in diameter under zero-wind conditions. Nozzle locations were such that as little as five knots of wind would cause the spray to cover all topside weather surfaces. The interim system for carrier flight decks featured quick connecting, light weight aluminum pipes with installed nozzles. On the flight deck, these could be laid out athwartship by a trained crew in five minutes, but they had the obvious disadvantage of causing the suspension of flight operations. New flush-mounted deck nozzles requiring shipyard installation have replaced the portable pipe arrangement on carriers, and for several years now, permanent systems have been installed in all new construction ships.
Associated with fallout is the base surge which occurs with an underwater burst. This is a rapidly expanding cloud or mist of water droplets emanating from the water column that rises after the explosion. The visible base surge expands from two to three minutes and then drifts downward until it is dissipated. The size depends on the yield of the weapon and other variables such as wind, the depth of the explosion and the over-all depth of water. The hazard from base surge can last from 20 to 30 minutes. Countermeasures against base surge are ship maneuvers to escape it, deep shelter for all personnel, and washdown and decontamination.
Summarizing the militarily significant effects of nuclear weapons, we find that:
The air burst is the “cleanest” and that it has no residual or delayed effects from transit or deposit radiation. Against an air burst, a ship must contend with air blast, thermal radiation, and initial ionizing radiation.
The underwater burst produces shock, transit and deposit radiation in the base surge, but it is limited in area.
The surface burst is the most versatile, producing all the effects of the air burst plus a hazardous fallout area which will move with the wind and can extend for several hundred miles.
Ionizing radiation is the effect most feared generally, probably because it is invisible, and little understood. It has operational significance in naval operations because of its ability to render personnel ineffective by death or radiation sickness. A CNO directive points out that the protection of personnel from radiation hazards and the decision to accept dosages in excess of those established for peacetime is a function of command. A commander who knows the effects of ionizing radiation can determine how large a dose his personnel shall be permitted to receive in carrying out his mission. For defense, he can use appropriate ship maneuvers, deep shelter, washdown, personnel rotation, damage control and decontamination procedures.
In a way, a ship has many advantages in combating radiation. First of all, it operates in a great disposal area, and radioactive wastes can be washed over the side into the sea with impunity. The sea is an inexhaustible source of water for the ship’s washdown system, and the water can be pumped from below the surface where it is not contaminated. The ship can maneuver at high speed to avoid fallout or base surge, and the construction of a warship with its compartmentation and seals is additional protection against inner penetration of radioactive decontamination. The primary means of preventing below-deck penetration is the “gas-tight envelope.”
The term “gas-tight envelope” refers to the damage control procedure which renders a ship fume-tight. Standard damage control practices, even in the most advanced steps of closure for enemy action, permit some fittings on a ship to remain open. For example, those which are vital to ship mobility and fire protection, such as sea suction valves, are classified as “William” and are closed only when it is necessary for the control or repair of damage. Ventilation fittings and certain access openings which supply air below decks are classified as “Circle William” and are closed for defense against nuclear attack to prevent the introduction of radioactive particles below decks. Their closure causes an immediate increase in heat and humidity in the ship’s interior—so much, in fact, that it is usually necessary to open them periodically for brief periods of relief. In some ships, vital spaces such as open boiler rooms and electronic equipment spaces cannot be closed off from air supply even in the event of nuclear attack. The only recourse for personnel in these spaces is to wear protective clothing and to rotate with others in deep shelter. The gas-tight envelope is established when “X- ray,” “Yankee,” “Zulu,” and all “Circle William” fittings are closed.
Today’s Operation Plan or Operation Order contains the commander’s views and guidance for radiation exposure applicable for the mission. This guidance should specify the casualty risks considered acceptable, and all ship and unit commanders should operate within this exposure limit. The injury that an individual will receive from radiation exposure depends on many factors: the initial dose, the amount of his body exposed, the period of time in which the dose is received, previous dose history, and the nature of other injuries sustained. The effects are not immediately discernible without the use of dosimeters which measure the intensity of the exposure.
The unit of measurement most commonly used now is the “rad” which is a unit of energy absorption of any type radiation, but which may vary with material, such as tissue or water. This is considered a better practical measurement than either the roentgen, which measures the energy absorption of X-ray and gamma radiations in air, or the rem, which is a unit of biological dose.
The upper safe limits of exposure are now considered to be 200 rad per day or 400 rad per month. This is the threshold beyond which many personnel will become combat ineffectives. For example, if, in a 24-hour period, personnel received 500 rad, they may become combat ineffectives in about 12 hours and many may die. If they received 10,000 rad, they would become ineffective in less than an hour and all would die. The above examples are termed acute doses and result from exposure of 24 hours or less. Protracted doses come from longer exposure during a period lasting from 24 hours to two weeks. A protracted dose of 500 rad would cause combat ineffectiveness within one week and many would die. A protracted dose in excess of 1,000 rad would produce ineffectiveness within four days and most would die. When combat ineffectiveness starts, and how long it lasts, however, is poorly understood— particularly in the case of protracted doses.
The general prudential rule is to prescribe as an upper limit not more than 200 rad per day and not to exceed 400 rad in a month. If the entire crew had earlier dose history, the guidance should be revised downward. If only a few members of the crew had prior exposure, they should be assigned to deep shelter General Quarters stations.
For detecting and measuring radiation, the Navy uses six main types of equipment. These range from the installed radiac on the open bridge of newer ships to the simple individual film badge. This variety of equipment is necessary, because there is no single radiation detection instrument capable of monitoring all radiological situations. The wide range of possible radiation levels and the different physical properties of various kinds of radiation produce measuring combinations beyond the capacity of a single instrument.
Navy radiac instruments can be divided into two general classes: the dose-rate meter, and the dosimeter. The dose-rate meter is a survey meter, usually the ion-chamber type, which measures the intensity of radiation (how “hot” an area is). The dosimeter measures the total dose of nuclear radiation absorbed over a period of time. These instruments can be compared to an automobile speedometer. The dose-rate meter is similar to the needle which indicates speed, and the dosimeter is similar to the odometer which shows miles travelled.
There are three primary types of survey (dose-rate) meters: the high intensity (Hi-R), low intensity (Lo-R), and alpha. Typical measuring ranges of geiger counters now in use are from 0.5 milliroentgens per hour to 500 milliroentgens per hour for the low range meter, and from 0.5 roentgens per hour to the 500 roentgens per hour for the high-range meter. These instruments are used primarily to measure gamma radiation. An alpha proportional scintillation counter is used to measure alpha particles.
Most radiacs measure dose rate within + 20 per cent, so the calibration of radiacs for safety monitoring need not be as precise as for experimental measurements. The ion chamber radiacs are calibrated by comparing calculated dose rate with the dose rate measured by the instrument. From this comparison, a correction factor is determined at various check points on the scale. The alpha radiac is checked against an alpha standard both before and after monitoring for alpha contamination.
The film badge is really a “photodosimeter” and consists of a film packet similar to that used for dental X-ray work. Ionizing radiation darkens film in much the same manner as does light. The amount of darkening is proportional to the energy of the radiation and the dose received by the film. The dose is measured by comparing unknown film density to known film density produced by similar radiation. Film badges are encased in conveniently designed holders which can be clipped to clothing.
Two more dosimeters complete the Navy’s typical measuring equipment. These are the pocket Lo-R dosimeter, and the Hi-R nonindicating dosimeter. The low-range pocket dosimeter is a very simple form of ion chamber about the size of a fountain pen. It employs the movement of a quartz fiber across a scale to indicate the dose received. As a rule, pocket low-range dosimeters will record a total dose of 200 milliroentgens. The high- range instrument is a glass dosimeter which requires a computer-indicator for its reading. This dosimeter contains a special prepared phosphate glass which can be worn around the neck like a dog tag. It operates in the range of from 10 to 600 roentgens.
The first requirement for defense against nuclear attack is adequate preparation before the attack occurs. Also, there are measures which should be taken during the attack to protect the ship from damage, and to limit the number of personnel rendered ineffective. And, last, there are post-attack maneuvers and countermeasures to reduce radiation exposure, and decontamination procedures to rid the ship of harmful radioactive particles. After detonation, a ship undergoes first an emergency phase in which survival is paramount. Here the commander depends on damage control, washdown, deep shelter, maneuver and rotation of personnel to maintain dosage control. Next, there is a phase of interim recovery during which some of the damage is repaired and the decontamination parties assess the radiation received. “Hot” spots are marked off so that personnel can regain and man vital stations with minimum risk. As the radiation intensity decreases, the commander can order his force to resume operations at or near the pre-attack level, taking necessary steps to reduce the long-term health hazard.
The naval commander at sea can take certain actions to reduce exposure of his units to nuclear attack. First, he can choose a suitable disposition for his force. There is no hard-and-fast rule in this regard, and more than likely his choice will be a compromise. The primary factors governing selection of force disposition are: mission, geographic area, weather, the speed and capabilities of his own force, and the nature of the primary threat. The best arrangement would be one in which not more than one ship would suffer severe damage from a nuclear burst and also one which would provide adequate antisubmarine and antiaircraft protection. Ship spacing therefore depends on the number of ships and the relative danger expected. Within these restrictions there should be maximum spacing between major units. Before an attack, the commander should designate both a moving rendezvous and regrouping instructions, usually the rendezvous point will be at a safe distance upwind from surface zero.
At the moment of attack, ships should turn to present the least profile to the fireball— their bow-on or stern-on aspect—and then take evasive action by first steaming at best speed away from the explosion. When clear of immediate fallout, ships downwind should then steam at right angles to the effective wind until clear of the medium range fallout area. Once clear of danger, ships should proceed to the rendezvous point, avoiding contaminated waters. During these maneuvers, individual units should assess and report damage and the intensity of radiation received.
Submarine nuclear defense presents some special problems. Against conventional weapons, the submarine defends against explosive forces which can punch a hole in the hull. Confronted by attack from units armed with conventional weapons, the submarine operates first to foil the attack and then to break contact with its pursuers. Tactics employed vary from deep submergence to the use of various decoys.
It is a different story when a submarine is threatened with an underwater nuclear burst. The lethal area of the underwater nuclear burst spreads conically toward the bottom, and the kill area at deep submergence is many times that at, or near, periscope depth. Moreover, the nuclear burst creates tremendous overpressures which tend to crush the submarine’s hull. It is easy to see that normal water pressure from deep submergence would complement the overpressure from a nuclear blast. Consequently, the basic principle for defending a submarine against nuclear attack is to avoid deep submergence.
Current submarine practice for defense against nuclear attack at sea calls for submergence to periscope depth and rigging for depth charge attack. If the submarine is close to the base surge or fallout, she should take an evasive course at best speed. This course would be upwind if the burst itself is downwind, and it would be normal to the wind direction if the burst is upwind.
A submarine in port has two main choices in the event of nuclear attack: to sortie or to remain in port. For sortie, the submarine should rig for dive and “flood down” as the depth of the channel permits. Diesel-powered submarines would probably sortie on battery, and “button up” outboard fittings. If the submarine cannot sortie, she should, if possible, submerge at the dock until all danger from nuclear attack is over.
There are several aids available to assist in making nuclear defense command decisions. Some can be determined from training exercises, other from study and understanding of nuclear weapons effects.
In routine training exercises, the commander can determine the time required to clear topside personnel and send them to deep shelter, as well as the time interval to reman at action stations. From experience, he can estimate how long it will take his monitoring teams to complete a monitoring survey or to read tactical dosimeters and evaluate the dose received. Determining the time to activate the washdown system, or to decontaminate a section of the ship depends on how contamination adheres to surfaces.
There are some general “rules of thumb” which can be usefully employed while waiting for more accurate measurements and predictions. For example, we know from tests that radiations are attenuated by distance and that neutrons and gamma rays are also attenuated by absorption in air. Neutrons from a large bomb reach out only about one and a half miles. Gammas from initial radiation of a five-MT bomb could be lethal at two miles. Therefore, at a distance of five to ten miles from a big bomb, thermal and blast effects are paramount.
Distance from the source is crucial, because radiation effects are governed by the inverse square law, and range of blast and shock effects vary with the cube root of weapon yield. In other words, a ship ten miles from a source of radiation will receive 1/100 of the dose rate received by a ship one mile from the source. Furthermore, while a 20-MT bomb is a thousand times as powerful as a 20-KT bomb, the damage from the blast extends only ten times as far.
Time is important because of the phenomenon of radioactive decay. If we double the time since detonation, the dose rate is down to one-half. In other words, if the dose rate on a ship is 100 r/hr two hours after the explosion, it will be 50 r/hr four hours after the explosion. Another useful estimate can be used in determining total anticipated dose. A gamma dose expected from indefinite exposure equals five times the present intensity multiplied by the hours since detonation. Hence, if in two hours some men should receive a dose of 50 r, and the dose rate reading at that time was 25 r/hr, they could anticipate 5X25X2, or 250 more r’s, if they continued working. The total dose that they would receive from indefinite exposure would be 50 r plus 250 r, or 300 r. (Rules on dose rate vs. time require that fallout has ceased, and that there has been no decontamination.)
Computational predictions of radiation intensity can give a more accurate basis for decisions, and can influence the degree of readiness to be maintained. Reports from ships at various distances from the radiation source can provide a pattern which will eventually form into a fairly realistic and accurate background for decision making. In each ship, it is a function of damage control to maintain a plot of radiation intensity versus i- time after the burst.
There are two general situations in predictive plotting, depending on the distance from a the detonation. If the ship is close to the explosion, the time of detonation will be obis served or felt, and radiacs will record initial radiation first. This will decrease for about one minute and will reach a minimum just e before fallout arrives. As intensity readings increase with the arrival of fallout, the plotted curve can be projected to show peak intensity. With a distant burst, the predicted time of peak intensity should be twice the fallout arrival time. After several readings, projections e on the radiation plot will give a predicted a peak intensity. This should be checked frequently, since vital actions such as washdown and evasive maneuvers can have radical effects on the estimate.
The Navy’s fear and awe of nuclear weapons has changed to understanding and respect. Nuclear defense bills are a standard part of n the ship’s organization, and drills in defense against nuclear attack are held frequently. The conditions which would prevail in a nuclear attack are hard to simulate, but as a rule, these drills are carried out with sober intensity. Monitoring teams don protective clothing and make monitoring sweeps with their geiger counters; decontamination teams actually scrub down marked-off “hot” areas, and the washdown system is tested despite the laborious after-task of cleaning salt water from topside equipment. Exposed personnel practice at taking deep shelter, and damage control parties zealously set condition Circle William in spite of the ensuing discomfort.
The introduction of nuclear weapons to sea warfare is an extension of steady scientific advance which has produced a number of so-called ultimate weapons throughout history. Naval forces have met the challenge of Greek fire, the ironclad, the rifled gun, the mine, the n torpedo, the submarine, and the airplane. At this stage of development of nuclear weapons, it appears that the adage “For every offense n there is a defense” will continue to hold true.