Leakers Happen

With the ongoing attacks on surface vessels in the Red Sea by the Houthis, the world is being graphically introduced to the concept of salvo warfare. In modern naval warfare, combat power is delivered in pulses of destructive power. As discussed in Fighting the Fleet: Operational Art and Modern Fleet Combat, the late Captain Wayne Hughes introduced this idea and developed the Salvo Equations to describe the phenomenon.[i]  With the Salvo Equations, Captain Hughes…

“…showed how modern naval combat follows a salvo model: opponents apply a pulse of combat power to each other in an instantaneous salvo exchange. A salvo exchange is an interaction of offensive combat power (e.g., mines, torpedoes, bombs, or missiles) and defensive combat power (e.g., surface-to-air missiles [SAMs], jamming, chaff, decoys). Combat power remaining from these interactions is applied against a target’s staying power (the number of hits of a particular weapon that a target can withstand and still be useful for combat purposes).[ii] 

The Salvo Equations are presented here for reference and are discussed in great detail in Chapter 1 and Appendix A of Fighting the Fleet:

When considering the a₃ and b₃ terms – the number of incoming missiles each side can destroy – how do we know how many missiles a modern warship with a primary mission area of area air defense, can destroy? These kinds of ships – ships like the U.S. Navy’s DDG 51-class guided missile destroyer, and the Royal Navy’s Type 45 destroyer – face the Houthi threat every day. So far, they have been able to defeat the weapons fired at them – anti-ship cruise missiles, anti-ship ballistic missiles, and suicide unmanned aerial drones – but how long can this last? How large of a salvo of anti-ship weapons is required before a warship can expect at least one weapon – a leaker – to get through?

The answer is both “it depends” and “surprisingly few.”

To understand how to quantify the answer, we turn to Appendix B of Fighting the Fleet, which is focused on the use of the Salvo Equations in support of force planning.[iii]  This process introduces the concept of “leakage rate.”  The leakage rate represents the rate at which the planner can expect enemy offensive weapons to get through the defensive systems of a modern warship – the anti-air missiles, electronic countermeasures (ECM), decoys, and close-in weapon systems (CIWS). The number of weapons that can expect to pass through the defensive systems of a ship can then be expressed as:

L = O + (O * l) – D

where:

“L” is the number of leakers

“O” equals the number of offensive weapons

“l” equals the leakage rate, expressed as a value between 0 and 1

“D” equals the number of missiles the ship defensive systems can expect to defeat

But how big is “D”? Surely the number of missiles a ship can defeat is a closely guarded secret! And, as one might expect, it is – so the approach this analysis will take is to assume that “D = O;” that is, that the ship can defeat as many well-aimed enemy weapons as are fired against it in a simultaneous salvo.

Since no system designed and built by mankind is perfect, we can assume that no ship defensive system is perfect[iv] – in this analysis we will assume a range of values for “l” to determine the number of enemy weapons required for at least one weapon to get through. Assuming a range of leakage rate values from 0.05 to 0.2 in increments of 0.05, we can generate the following table, with the results rounded to the nearest integer:

This analysis does not pre-suppose the class of ship or the limitations the ship combat system may have in defending against a number of simultaneous targets. Note that even a ship that can defend against more than ten simultaneous targets, and that has a nearly perfect ability to defeat any well-aimed missile, should not be surprised to experience a leaker with a salvo size as small as ten incoming missiles.

The warships in the Red Sea that have been protecting shipping and engaging with Houthi-launched missiles and drones have so far been successful in defeating all the weapons fired at them – although at least one, the USS Gravely, had to employ its Phalanx close-in weapons system (CIWS) to defeat one missile[v], because, in modern salvo warfare…leakers happen.

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Anthony Cowden is the Managing Director of Stari Consulting Services and co-author of "Fighting the Fleet: Operational Art and Modern Fleet Combat," all royalties from which go to the Navy/Marine Corps Relief Society.