The recent Navy League show in Washington was dominated, at least visually, by the DD-21 program, and particularly by a massive full-size mockup of its 155-mm gun, in a housing shaped to minimize radar cross-section. United Defense, which has long been responsible for U.S. naval guns (many of them under the earlier name of FMC), displayed a variety of shells, including a mockup of a guided shell with a millimeter-wave seeker. Lockheed Martin showed a naval version of the global positioning system (GPS)-guided multiple launch rocket system (MLRS) that it has developed for the Army (but which the Army seems unlikely to buy). The rocket can be quad-packed in a standard Mk 41 vertical launcher cell. The company also displayed a first model of the advanced land-attack missile it hopes to sell the Navy.
The gun may well be the key to the DD-21 program. For years, the Marines tried in vain to get the Navy to retain the sort of shore bombardment firepower they needed to overrun a defended beach. In this battle, the loss of the battleships was probably the final straw, but earlier the Marines had failed several times to get a special-purpose landing fire support ship (LFS), most recently when they gained Congressional support for the project in 1984-86. Historically, the U.S. Navy has much preferred general-purpose ships. That is quite reasonable. Ships take a long time to build, and they last a long time. It is totally unrealistic to imagine that the conditions which engender a ship in, say, 2000 will still hold true 30 years later, when ships of the class reach early mid-life. Skeptics may want to remember that conditions in, say, 1942 were rather different than they had been in 1912, or, for that matter, in 1972. The ships that were still useful were those with the most open architecture. It is no accident that Essex (CV-9)-class carriers, which were adaptable because they were built around big open hangars, had such long lives (and, incidentally, outlasted contemporary British carriers, whose closed hangar designs were far more difficult to modify to take newer aircraft).
The Marines enjoyed considerable fire support during and after World War II largely, though not entirely, because at that time the gun was the fleet's general purpose weapon. The same gun (which might be thought of as the same launcher) was used for surface fire, for shore bombardment, and for antiaircraft fire. A decade or so after the war, however, that flexibility was gone. Guns were good for firing at other ships or at shore targets, but hostile aircraft were increasingly the preserve of missiles-and hostile aircraft were the main threat to the fleet. It was no great surprise that all-gun ships were retired, or that the number of guns on board ships armed with antiaircraft missiles shrank dramatically, to the point where there were not enough for effective surface fire or for shore bombardment. Indeed, from about 1960 on, the Navy and the Marines actively considered shore bombardment missiles that could be fired from standard missile launchers. An adapted Army Lance missile was a major candidate during the mid-1960s.
Ultimately the Marines realized that no such missile could really be satisfactory. Ships could carry only very limited quantities, and they could not deal with the sort of pop-up targets that ships so often engaged during World War II, simply because they did not have enough. It also became clear that, whatever claims might be made, large missiles were very difficult to transfer at sea.
The Marines realized that they had to change their strategy. Classic amphibious assault could be likened to frontal assault on land, as in World War I. To some extent helicopters made flanking assault possible. The fast air cushion landing craft, which could ride over most kinds of beaches, could help. Even so, flanking a fixed enemy position still required some degree of fire support directed at the beach.
In the 1980s, the U.S. armed services began to follow the Soviets in distinguishing between tactical and operational levels of maneuver or combat. Tactical maneuver was conducted more or less in contact with enemy forces; a flanking attack in such circumstances, for example, would be a tactical maneuver. Operational maneuver was maneuver out of contact. The concept embraced an army's maneuvers between actual battles, and the Marines had a particular kind of operational maneuver in mind.
As long as Marines were offshore beyond an enemy's horizon, they could maneuver quite freely. They could land anywhere along a shore, a degree of flexibility enhanced by using amphibious vehicles, such as air-cushion landing craft, which could tolerate a very wide range of beach conditions. At first, the Marines saw this flexibility mainly as a way of enhancing the element of surprise: an amphibious force standing far offshore could attack anywhere along hundreds of miles of coast line within 24 hours, and any defender would be hard-pressed to concentrate troops on the right beach in time. This was the over-the-horizon (OTH) assault concept popularized during the 1980s.
Now the idea is being pushed further. The target is generally inland of the beach. Once it has been selected, fast-moving Marine forces can come ashore at widely-dispersed places, moving independently toward concentration at the target. This is equivalent to the infiltration tactics first developed on land by the Germans during World War I as an alternative to murderous frontal assaults (it was generally impossible to use flanking tactics because the front lines extended for hundreds of miles).
Now the rub. The fast-moving forces cannot take much with them. The old kind of assault was designed to seize a beachhead, on which material could be built up in preparation for a push inland. If forces do not concentrate until they reach the objective inland, however, then there can be no concentrated dumps. Small amounts of material can be dumped along the paths the dispersed forces are to take, but the less the better (this concept also depends on the infiltrating forces having GPS or some equivalent form of land navigation).
Infiltration takes care of the threat of coast defenses-at least in theory; the Marines probably will be able to land without a preparatory naval bombardment. Much of the weight the Marines normally carry inland, however, is supporting firepower, such as a battery of six 155-mm howitzers and ammunition. If the new tactics are to succeed, the Marines must get much of their fire support somewhere else-probably from the sea. Thus the gun on board the DD-21 is intended for a new kind of role, actually replacing the shore-based artillery the Marines normally take with them. Moreover, if the Marines really split up into small units, then it is not clear that supporting firepower can ever be split up sufficiently. Seaborne support becomes part of the new tactics.
This is very different from past naval gunfire support. Like the howitzers normally taken ashore, DD-21s must be available, on call, 24 hours a day until the Marines can seize their major objective and concentrate resources there. To avoid close-in hazards, any DD-21 must be able to operate from well out to sea, firing in very bad weather. Since calls for fire will come primarily from the dispersed Marines ashore, she needs excellent communications and position-keeping, both now possible using space systems (communications and GPS). The design requirement for the ship includes a rate of fire at least equivalent to the usual six-gun battery ashore, even though the ship has only a limited supply of ammunition. Unlike missiles, shells can be transferred at sea. Presumably it follows that DD-21 needs the ability to replenish her ammunition very quickly. There would seem to be a larger requirement for a floating ammunition dump near the ships, in the form either of combatant ammunition ships (AE) or of the much-discussed mobile offshore base.
Given the gun, the question is whether it can do more than attack targets ashore. The millimeter-wave seeker may offer a valuable anti-ship capability. Without it, shells are dispatched to designated GPS coordinates, which is probably entirely satisfactory for more or less static ground targets. Clearly there is also the possibility, mooted in the 1970s, of providing a shell with an antiaircraft seeker (for a time the U.S. Navy was developing an infrared-guided five-inch shell).