Anti-submarine warfare (ASW) is probably the most complex form of maritime conflict. The search for solutions of the “submarine menace” tends to be focussed on technological “fiXes” – more powerful and longer-range means of surveillance, faster and more accurate detections systems, and stand-off, high-probability-of-kill weapons. Little about the technologies of modern submarine and anti-submarine warfare is comparable with the methods of history’s first ASW campaign, World War I. By contrast, ASW strategies have basically remained the same ones that were first tried out more than 70 years ago. What then are the fundamental choices of ASW strategies that provide the framework for the exploitation of ASW technologies.
Anti-submarine warfare (ASW) fought mainly at sea, is aimed at defeating the war-fighting purposes of the submarine. ASW is practiced at three levels of planning: strategic, operational, and tactical. Basic ASW strategies are of three kinds: (1) destruction of enemy submarines (2) containment of them, and (3) limitation of their war-fighting efficiency. The operational )eve) of ASW planning is concerned with where and how to destroy, contain, or limit the efficiency of hostile submarines. The operational choices are whether to defeat the submarine at (1) its sources, i.e. operating bases and construction yards, (2) in transit, particularly in “chokepoints”, or (3) in the patrol areas themselves. ASW tactics are concerned with the local coordination of platforms, weapons, and sensors in the area of encounter itself. Tactical ASW consists of four phases: (1) surveillance and reconnaissance, (2) detection, (3) tracking, and ( 4) attack.
As background, ASW emerged as a strategy preoccupation for naval planners during World War I. Pre-war defensive measures against the “submarine torpedo-boat” were little more than ad hoc adaptations of tactical procedures that had been adopted by most fleets to guard against the other “sneak attack” weapon, the torpedo-boat. The principal offensive measure relied on the warship’s superior speed to run down and ram his underwater opponent; defensive measures included sailing a “zig-zag” course and, in port, the erection of physical obstacles (such as harbor booms and blockships, and antitorpedo nets), and night-time illumination.
The pre-1914 failure to anticipate the strategic scope of the submarine problem can be attributed to the dominant “image” of the submarine. First, the submarine was expected to seek out naval targets; few Allied or Entente naval planners on the eve of World War I foresaw that the submarine would be a commerce-raiding weapon first and an anti-fleet weapon second. Furthermore, most naval professionals doubted that the submarine would be more than a “nuisance.” Because of its inferior speed, limited combat radius, and near-blindness when submerged, the submarine was expected to limit its wartime contribution to coastal defense and occasional scouting missions on behalf of the fleet of battleships and battlecruisers. Six months into WW I the prognosis of a quick conclusion had collapsed – so had the image of the submarine as an occasional nuisance. At sea, the pre-war plans for a “decisive battle” gave way to the search for long-term ways and means for defeating the most difficult opponent in recorded Naval history.
All things equal, the preferred ASW strategy is one that results in the physical destruction of the submarine — the outcome is permanent and, with the underwater opponent eliminated, resources can be released for other wartime duties. Strategies of destruction have also proven to be the most difficult and risky, depending on the quality and quantity of the opposing submarine force, sinking submarines may take more time and tie up more sources than can be afforded. A different kind of risk may be associated with “strategic” ASW against strategic missile submarines. The destruction or even the threat of destruction of this particular type of submarine might undermine the stability of mutual strategic deterrence, and could force a decision to “use-them-instead-of-lose-them.”
The preferred strategy of destruction at source is aimed at submarine operating bases, construction, repair and maintenance yards, and industries that manufacture critical components. The single most important advantage of this approach is that it circumvents ASW’s most difficult problem: finding the opponent. Unfortunately from the point of view of the ASW strategist, enemy submarine bases and building yards also tend to be heavily defended and can therefore usually only be attacked at great risk to one’s own forces. The allied naval planners of World War I shared President Woodrow Wilson’s “despair of hunting for hornets all over the sea when I know where the nest is.” But very few among them shared Wilson’s willingness to “sacrifice half the navy, Great Britain and we together have, to crush the nest. .. ”
The practice and planning of destruction at the source has known four methods: (1) physical seizure and occupation of bases and yards, (2) fleet bombardment, (3) aerial bombardment, and ( 4) mining. For reasons that are obvious, the first method is the most decisive one. Yet, for reasons equally obvious, the physical seizure and occupation of enemy submarine bases and yards is likely to be attempted and crowned with success only if they are part of a general campaign of territorial conquest. The Anglo-American and Soviet occupation, in 1944-45, of the French and Baltic coastal areas, respectively, deprived the German U-boat fleet of key operating and construction sources. This outcome was not the result, however, of a deliberate ASW strategy, but instead the “bonus” reward of the Allies’ general advance.
Excepting the sporadic shelling, by the Royal Navy, of Germany’s U-boat bases on the Belgian coast in World War I, the strategical choice of destroying the submarine menace at its source through fleet bombardment has historically been stymied by the fear of disproportionate losses.
The destructive record of mining and aerial bombardment of submarine bases and yards is a mixed one. During World War I a single U-boat was lost among the more than 44,000 mines that were scattered in the Heligoland Bight; altogether 14 U-boats were destroyed in their Baltic Sea training grounds during World War II. Arguably, the most productive result of the Baltic mining offensive was the interference with crew training and new construction work-up, i.e. with the U-boats efficiency, and may have prevented 20 Type XXI U-boats from becoming operational.
Especially disappointing were the results of the World War IT air offensive against the operational and industrial sources of the U-boat. Principal operational targets were the concrete submarine shelters on the French and Norwegian coasts. Even the heaviest bomb of the wart the 12t500 pound “Tallboyt” failed to penetrate the roofs up to eight meters thick. One Uboat was destroyed at its base in Trondheim, Norway in July 1943. Post-war tests by the Americans indicated that a future air assault against “hardened” submarine pens would probably require nuclear weapons.
Industrial sources for the Allied bombing campaign included four broad target sets; (1) the U-boat building yards themselves (2) centers for the manufacture of key components (e.g. the Hagen center for the construction of batteries) (3) the German industrial and transportation system generally, and (4) the labor force. The British Bombing Survey Unit concluded that the bombings directly and indirectly contributed to a production loss of 111 U-boats and that another 42 operational units were destroyed in port. The reasons for the low profitability of the anti-source, bombing campaign were (1) the inaccuracy of bomb-laying techniques (2) the enemy’s better-than-expected recovery capabilities (3) the generally efficient German air defense system, and ( 4) the “cyclical” pattern of the •direct” offensive against U-boat penst yardst and other facilities.
Because of the difficulty of destroying the submarine at the source, the ASW planners are usually compelled to find ways to defeat it at sea, including the submarine’s transit and patrol areas.
A key determinant for the success of a strategy of destruction in transit is local geography, i.e. the length, width, and depth of the “chokepoint. • The collective ASW benefit of a long and narrow area of submarine passage is” (1) a high predictability of the submarine’s comings and goings (2) multiple opportunities for attack, and (3) minimum submarine escape volume.
The opposite conditions usually exist if the submarine’s patrol area is in the high seas. It follows that an ASW strategy aimed at finding and destroying the opponent in the open ocean is highly dependent on strategic intelligence about his general whereabouts, strength, and direction of movement. Normally a hunt-and-kill strategy without the benefit of strategic “cueing” has historically shown to be a cost-ineffective search for a “needle in the haystack.”
Strategies of destruction in the transit areas have generally relied on minefields, sometimes backed up by mobile surface and air patrols that are linked to “bell-ringer” detection devices.· A successful ASW barrier system will destroy few enemy submarines, however. After the first few losses, submarines are likely to be diverted to a less dangerous route of passage; if this does not exist, they are effectively contained. The latter was the fate of the submarines of the Soviet Baltic Fleet during World War ll. From the spring of 1943 until the capitulation of Finland in September 1944, the German-Finnish “Walross” barrier of steel nets, mines, and mobile patrols across the Gulf of Finland excluded the Soviet underwater flotillas from the Baltic Sea.
Destruction strateaies in the oatrol areas comprise “offensive” hunter-killer (HUK) and “defensive” armed-escort of the targets of the submarine, i.e. the convoy system. Between the two, falls the system of “protected lanes.” This last strategy combines intensive hunter-killer and close escort operations in the approaches to ports and harbors where seagoing traffic is “funneled,” and where enemy submarines may be expected to concentrate. Although a failure in the past, some Western naval planners today believe that, between much improved detection capabilities and a shortage of convoy escorts, the strategy can and must work.
Today, as in the past, the prospect of a hunter-killer strategy is vitally dependent on strategic cueing. During World War ll, Allied “hunting groups” achieved spectacular successes thanks to two sources of “strategic” intelligence: (1) the interception and location of U-boat radio traffic through high-frequency direction-finding and (2) the de-cryption of the U-boat fleet’s “Triton” cipher. Contemporary strategic intelligence about enemy submarine movements still relies, in part, on communication interception, but ASW plans cannot depend on a repeat of the Triton-breaking success of World War II’s “Ultra” group. Instead, billions of dollars and rubles are being invested in extremely long-range acoustic and non-acoustic ocean floor-mounted and satellite-carried ASW “early warning” systems.
Today, the convoy system is usually labeled a “defensive” ASW strategy and considered “inferior” to “offensive” HUK. The two world wars show that (1) the convoys were the single most successful means for defeating the purpose of the U-boat — to sever the Allies’ economic and military arteries, and (2) ships and aircraft on convoy escort duty destroyed more submarines than did their counterparts engaged in HUK operations.
Destruction of the enemy’s submarine is a bonus; the essential purpose of the ASW strategist is to defeat the warfighting purpose of his opponent. Containment strate&ies have historically depended on physical obstruction of the submarine’s movements, including minefields and nets.
The advantage of an ASW strategy of containment is twofold: (1) it minimizes the risk of casualties that is part and parcel of destruction strategies, and (2) it reduces the need for current intelligence about the submarine enemy’s plans and movements; in theory at least, all the ASW defender needs to do is to find the right “cork” to “bottle up” the opponent. The disadvantage of containment is also twofold: (1) it is quite difficult to create a hermetically-sealed barrier, and (2) containment schemes are likely to tie up forces that are badly needed elsewhere.
Most close-in A5W containment schemes have relied on minefields. Few have proven effective. Success in mine warfare ultimately depends on the relative stamina of the two sides, i.e. the relative persistence of the mine-layer and the mine-clearer. The Allied mine-laying campaigns of the two world wars failed to contain the U-boats inside their bases because the Allied navies were unable or unwilling to patrol the fields within easy reach of enemy counter-attack, and prevent the Germans from clearing a safe passage through the cordon.
Static containment strategies without the presence of mobile reactive forces have proven equally unproductive in the submarine’s transit and patrol areas. A determined submarine opponent will find means to find or “create” a crack. The most famous anti-transit barriers of the two world wars were the Dover and Northern mine “barrages.” The first involved a combination of minefields and “tripwires” laid across the English Channel; the second depended on tens of thousands of mines planted in the Greenland-Iceland-United Kingdom “gap.” Neither were effective. Four-to-six U-boats were lost on the Dover barrier and a single U-boat may have fallen victim to World War ll’s northern barrage.
Strategies for Limiting the Submarine’s War-FiKhtinK Efficiency. If the enemy submarine cannot be destroyed or contained, yet is denied the full use of its destructive capabilities, the ASW strategist has achieved his purpose. The choice of efficiency-Iimitin& strate~es begins at home, and is dependent on the war-fighting purpose of the enemy submarine fleet. For example, if the purpose is economic strangulation, the ASW defender may counter by reducing his dependence on seaborne commerce (by food rationing, and boosting domestic sources of supplies). If the threat is one of strategic missile attack, various passive and active “damage limitation” measures are possible.
Production efficiency may be reduced by aerial “harassment raids.” aimed at forcing yard workers to repeatedly stop work and seek shelter. One of the hoped-for effects of the Allied city bombings was the lowering of the morale and hence fighting efficiency of U-boat crews.
Efficiency-limiting strate~es in the transit to patrol areas are designed to minimize the submarine’s productive patrol time. Forcing the enemy to use a more time-consuming route does this. For example, the success of the “improved” Dover Mine Barrage of 1917-18 lay in the forced re-routing of the U-boats via the more distant waters between Norway and Scotland. Broad area search and surveillance by patrol aircraft may also delay submarines in getting to patrol areas. During World War II, the fear of airborne discovery forced the Uboats in transit through the Bay of Biscay to spend increasingly more time at slower underwater speeds.
The submarine’s productive period in patrol areas is determined, in part, by the amount of fuel and weapons it carries. Thus, interfering with its logistics infrastructure may be important. The best known illustration of this particular strategy is the systematic Allied campaign of World War n to destroy the “Milch Cows” — the U-boats replenishment submarines.
Summary: The table below compares the destructive productivity of different ASW methods during the two world wars. Not shown are submarine losses due to scuttling, collisions and other marine accidents, capture, or own forces.
Jan S. Breemer