A need to provide tactical support to u.s. air and ground forces stationed overseas gives rise to an important submarine mission. That mission is the attack of land targets far beyond the range of the submarine guns of World War II. Two types of delivery systems have emerged in the past forty years as candidates for this mission -either long range ballistic, or air-breathing “cruise11 missiles. The nature of land targets and probable enemy countermeasures to be encountered greatly favor the use of the ballistic missile over the cruise missile.
The U.S. Navy has recognized two separate types of land-attack missions. The first to become operationally deployed was the Polaris system for the strategic or deterrent mission. The first Polaris mission was conducted in late 1960. MorP recently, a weapon system was developed for the tactical land-attack mission -the TOMAHAWK cruise missile. Now, a more effective submarine land-attack system needs to be defined for tactical nuclear war.
The characteristics of the missile payload selected for a land-attack mission is crucial to the design of the weapon — its size, weight, range and speed. An early determination is therefore required of the types, characteristics and locations of potential targets, the extent of damage desired, and the yield and placement of the payload.
Of equal importance is the missile-carrying capability of the submarine. The objective of a tactical support mission is to effectively participate in a battle. To do so it must rapidly deliver payloads to one or more selected target complexes. A target complex is normally composed of both area and point targets. Typical area targets such as airfields, troop concentration areas, ports, industrial centers, and transportation hubs may cover several square miles. These are generally “soft” targets. They will normally require more than a single detonation in the target area. Point targets include specific installations such as a command center, a communication center, a dam, or a bridge. They may be either “hard” or “soft.” While a single hit may be all that is required, at least two launchings may be required to attain hit assurance, and in a given battle area several point targets may be designated. Therefore, to provide tactical support in a given battle situation the submarine must carry sufficient weapons to meet the needs for coverage of both area and point targets to effectively deter enemy air and ground force employment.
Having determined the nature of likely tactical targets, missile range requirements may be determined from the geographical distribution of land masses and submarine operating areas. Figure 1 represents one possible and very important target complex — the Bloc areas in Europe. Here lie the probable routes that Soviet land forces would take if they were to invade Europe in the future.
The cross-hatched areas shown in the figure extends approximately 1,200 n.m. from south to north — from the Mediterranean to northern Finland. Since target coverage increases rapidly with increased missile range, submarines with 1,500 n.m. missiles could attack targets anywhere within the Bloc areas from off the Atlantic coast or from the Mediterranean and Norwegian Seas. In fact, 1,500 n.m. missiles launched from the Norwegian Sea could even reach the Leningrad and Moscow areas.
An important consideration in the design of a submarine tactical missile is to achieve the longest range and shortest flight time to target with the lightest and smallest missile capable of carrying an effective payload. Payload weight has a tremendous effect on the range and speed (time to target) performance of both cruise and ballistic missiles. As payload weight is reduced, a missile’s speed and range performance improves. To illustrate the effect of payload weight on missile weight, a missile capable of carrying a payload weight of 1,000 lbs. to a range of 1,500 n.m. might weigh over 20,000 lbs, whereas it migh~ weigh only about 3,500 to 4,000 pounds if it carried a small nuclear payload. Since missileenvelope volume is approximately linearly related to weight, the volume of the heavier missile would be about 5 times that of the lighter missile. Fortunately, light-weight nuclear warheads are available.
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Another important consideration is missile accuracy. It is determined by the nature of the targett the degree of damage desired, the characteristics of the payload detonation, and detonation placement relative to the target. There are several effects of nuclear detonation to consider — blast, shock, heat and thermal radiation. All of these factors must be considered in determining missile-accuracy requirements.
With a missile-accuracy requirement established, the missile guidance system design must allow the missile to deliver its payload within the accuracy limits pertaining to specific types of targets. There are four basic types of guidance systems; inertial, map matching, homing and a combination of these. Inertial svstems are passive. They do not subject missiles to early detection by electronic intercept means. They do tend to drift — to gradually deviate from their initial settings. For that reason they are best used when the duration of powered flight is brief as in the case of a ballistic missile. ~ matching techniques are usable only over the land portions of cruise missile routes, but are not normally applicable to ballistic missiles. _ They update inertial guidance position and azimuth. Three types of map-matching may be employed -contour matching, optical image matching and earth radiation imagery matching. In contour matching, the missile’s radar altimeter measures the contour of the land over which the missile flies. The guidance system then compares the results with an earth contour map stored within the missile’s guidance unit’s memory to determine the missile’s geographic position and heading. This is the technique used in the TOMAHAWK’s “TERCOM” system. Contour matching provides fair to good accuracy if earth contours are reasonably distinctive. Since radar altimeters radiate energy there is a likelihood that the missile will be detected while still distant from the target. Optical map-matching is a passive system used with TOMAHAWK with conventional payloads to provide greater terminal accuracy against point targets. It achieves its accuracy by viewing portions or the terrain over which the missile rlies with an electro-optical device. The guidance unit then compares the observed imagery with stored photo-reconnaissance imagery previously taken along a pre-planned rlight path. A similar map-matching technique uses imagery obtained rrom measurements or earth radiation. In all types or map-matching, the missile route must be pre-planned, ror it is necessary that the missile guidance unit contain within its memory the basic map data with which mid-course observations are to be compared. Terminal homing systems are target and rlight-path dependent. The primary use of terminal homing systems is to increase delivery accuracy against selected targets or target types. Types or sensors used in such systems include radar, electro-optical/inrra-red, and radio/radar intercept techniques. Homing systems have limited application to cruise missiles used in theater tactical warrare. Homing systems ror tactical ballistic missiles are generally infeasible because of reentry body heating and the resultant ionization during the approach to the target. These erfects appear as the missile enters the earth’s atmosphere at about 400,000 reet and hamper the performance of the homing sensors. In addition, the inertia of the reentry body and the short time available ror correction or reentry path tend to make ballistic missile homing systems relatively inefficient.
An important characteristic of tactical warfare is “movement.” Therefore, payload delivery systems designed ror tactical combat must be time-sensitive, possess rapid targeting flexibility, short delivery time-to-target, and adequate accuracy to negate specific targets. With regard to targeting~ each missile should be capable or being targeted (or retargeted)• within. for example, a minute to any target within range. Map-matching guidance systems applicable to landattack cruise missiles such as TOMAHAWK do not permit this. Map-matching requires that at launch the guidance memory unit contain stored over-land route data (whether contour or imagery) to which observed data can be compared. This stored data is provided launch ships for selected over-land routes on computer media tapes or disks. Each route is prepared weeks or months ahead of time for a specific route to a pre-selected target. This stored data is inserted into the missile guidance unit just prior to launch. In addition, the ship must plan the over-water route to a designated sea-land boundary, and this route information must also be input to the guidance system and married to the over-land route data.
An outstanding feature of inertially guided ballistic missiles is complete flexibility with regard to last-minute target assignments or changes. Solution of the pure inertial guidance problem for ballistic missiles is mainly dependent upon inertial reference inputs, launch point and target geographical coordinates, and stored missile guidance system equations. Modern computer mass-memory storage units are very small in size but large in memory capacity. This now permits most of the traditional “fire control” functions to become part of the missile guidance and control system. As a result, the only manual inputs required are target geographical coordinates. Inertial system delivery accuracies to ranges of about 300 to 1,500 n.m. are of the order of 1/8 to 1/2 mile.
Missile attack reaction time — the sum of launch preparation time and missile flight time — greatly favors the ballistic missile over the cruise missile. Launch preparation time for modern ballistic missiles is measured in seoonds, whereas, launch preparation time for a TOMAHAWK is of the order of 10 to 20 minutes because of required on-board pre-flight activities. The time of flight for a ballistic missile to a target at 1,000 n.m. is of the order of 10 minutes as compared to 2 1/2 to 3 hours for the cruise missile. Thus, the attack reaction times compare as 10 minutes for the ballistic to 200 minutes for the cruise missile. The significance of this is that aircraft at an enemy air base, for example, may be long gone before the cruise missile gets there.
As to vulnerability, cruise missiles are subject to anti-aircraft defenses. These include electronic counter measures and weapons ranging from shoulder launched homing missiles to more elaborate SAM defensive systems. On the other hand, it is nearly impossible to provide defenses against ballistic missiles in the battlefield.
The “Sherwood Forest” arrangement of vertical launch tubes for ballistic missiles was first developed for POLARIS. The POLARIS submarine was readily achieved by cutting a SKIPJACK hull in half and inserting the launch tube section. The same concept is viable for providing a new tactical ballistic missile land-attack capability. Missile design should not be compromised by requiring that it be enclosed in a capsule and made capable of torpedo tube launch as is the case of TOMAHAWK. A vertical launch system will readily allow for growth including greater range and payload, and features such as stellar guidance mid-course update, if and when greater performance is required.
Now is the time to initiate design studies leading to an advanced submarine tactical ballistic missile, land-attack weapon system with immediate launch and fast attack-reaction-time capabilities, complete targeting flexibility, small nuclear payload, inertial guidance, at least 1,500 n.m. range, multiple vertical launch/storage tubes, and provision for missile growth. Such a .system will reduce the need for TOMAHA\~K missile over-land route reconnaissance and preplanning, and over-water route planning prior to launch. Further, ballistic missiles will present no conflict/deconfliot problems in a task force environment.
An additional consideration: the matter of payload delivery accuracy may come up. The answer is that ballistic missile inertial guidance accuracy appears to be adequate. Considering only blast effect, “The Effects of Nuclear Weapons, Edition 3, 1977,” gives the following data:
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psi will take care of any tactical force and its equipment. Thermal and radiation effects will finish them off!
William P, Gruner
