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April 2002 Excerpt

Stealth—The Hidden Pillar
Organic Mine Countermeasures—Signature Control for Force Protection Against Sea Mines




By Michael P. Schilt, reprinted from Surface Warfare Magazine

WEST BETHESDA—One of the United States Navy’s core capabilities is “Assured Access.” When command authority wishes to project power, it is the Navy that must acquire and maintain access, both for projecting the power inherent in forward naval forces, but also for enabling the flow of combat elements and logistical support crucial for joint and coalition forces.

Sea mines are the asymmetric threat that the enemy will deploy to deny access. Clearly sea mines are the alligators.

Essential to the successful execution of these missions and the maintenance of assured access are the elements of mine warfare (MIW). Traditionally, mine warfare has consisted of a naval mining capability, executed by employing sea mines, and mine countermeasures (MCM), currently executed by a “dedicated” force triad of air, undersea, and surface MCM elements, dedicated to responding, when required, for MCM efforts world-wide. A newly emerging capability, “organic” MCM (OMCM), is being added to supplement the dedicated forces to ensure deployed battle forces, when faced with an emerging mine problem, will have an inherent capability to begin conducting the required battle space surveillance and reconnaissance as well as execute a limited mine neutralization effort while dedicated MCM forces flow to the location. The nature of the development of the next generation of MCM systems has allowed the Navy to embed these capabilities in the battle group. There are seven OMCM hardware system pillars that will provide the Fleet with the on-site capability for successfully providing access. OMCM is typically thought of as finding, classifying, and avoiding sea mines (with limited neutralization, where necessary).

However, while the embedding of organic MCM capability within the battle group has garnered significant attention, an existing pillar, one that has received little emphasis, has languished. The existing organic pillar, one that significantly reduces the vulnerability and susceptibility of U.S. Navy ships and submarines through force self-protection, is the control and maintenance of the ship’s acoustic and magnetic signatures. Organic signature control has been given little exposure and emphasis, and in fact, ships and submarines today are usually unaware of their susceptibility to targeting by the detection systems of sea mines.


This article recounts the near catastrophe caused by the interaction of USS Princeton’s acoustic and magnetic signatures and the sea mines sown by the Iraqi forces in the Persian Gulf. From a signature perspective, we will discuss the Navy’s current status regarding signature control and MIW, and share recent progress made in elevating the emphasis and priority placed on the hidden pillar of OMCM.

Sea mines are cheap. Yet the damage caused to a ship by a sea mine can be hundreds of millions of dollars. This financial aspect plus the psychological/ public relations aspects of asymmetry are what is most appealing to our potential adversaries. The billions of dollars invested in the Aegis Program effectively reduced the advanced fighter risk and minimized the ship point defense problem. The inordinate risk from sea mines could be much reduced if just a small portion of that investment were realized in ship point defense against mines.

Since 1950, the U.S. Navy has lost more ships to mines than to missiles, torpedoes, or bombs as shown in Figure 1. In fact, the enemy investment of $15,000 in sea mines caused in excess of $167M in damage on the Princeton and Tripoli alone, and they indeed were successful in denying Fleet access!

Figure 1 also shows a photograph of USS Princeton after she detonated a Manta mine during the Iraqi war. Had the sea state been only marginally higher, the Princeton story may have been much worse. She was 35 miles off the coast of Kuwait and at slow speed when the Manta exploited her acoustic and magnetic signatures triggering her denial of access for the duration of the war. In fact, one might say we were pretty fortunate she actuated a Manta. A Manta is a small mine with a relatively small warhead. Think of how this story could have been different if the mine type she actuated was one of the much larger types the Iraqis had. We learned much from the Gulf war; first, that far more influence sea mines were used than expected, and secondly, signature control is the point-defense MIW-MCM Program that addresses the current influence mine threat to Naval ships and should be a cornerstone of today’s mainstreaming mine warfare defense.

There was great interest in knowing the safe operating depth and distance to influence sea mines immediately following the USS Princeton catastrophic encounter with the Manta mine. The U.S. Navy did not have a measurement capability to range ships in the Gulf and had to borrow a range from an ally. Shortly after the war, Congress mandated the U.S. Navy obtain ranges that could be deployed in any operational area for Fleet use. Six forward area combined degaussing and acoustic ranges were purchased and delivered in 1996. To date, only one of these six has been deployed and used—and only for MCM ships in the western Pacific.


All ships emanate an acoustic and magnetic signature. Various machinery components contribute to the ship’s acoustic signature from hull pressure in the very low frequencies, to different machinery items in the mid-frequencies, and to cavitation noise in the high frequencies. Depending on the type of mine, the entire acoustic spectrum can be targeted by influence mine sensors. The mine actuator circuit may not only look at the signal level but also at the rate of change of the signal. This rate of change is a function of the ship’s speed and proximity to the mine as it passes by. Thus, trying to be “loud” in hopes that mines will detonate before the ship approaches close enough to be damaged just won’t work. If being “loud” won’t work, then the only logical approach left is to be “quiet” or stealthy. There are many ways for a ship to do five knots with different machinery configurations. Some variations result in significantly different acoustic signatures. Correct training in ship operation and training in current signature information can significantly reduce susceptibility to mines.

The U.S. Navy has made significant acoustic and magnetic silencing investment in ship designs that should markedly reduce ship susceptibility to influence sea mines. But little has been done since the Gulf war to use the silencing investment and embedded signature control capability within the U.S. Fleet to validate that these silencing efforts have been maintained and correctly operated to reduce our ships’ susceptibility to mines.

In today’s environment, against a known percentage increase in threat, we have to ask, “are we sending our ships in harm’s way without knowing a safe operating configuration based on current magnetic and acoustic signatures?” Each ship should have graphs, as depicted in Figure 2, that provide the ship critical information for safe operation.

Currently, the type of information displayed in Figure 2, is not available. But this is essential for safe operation in today’s proliferated threat environment.

Officers and Sailors often do not know that most ships lost to sea mines are not mine hunter ships. Sea mines target and exploit the acoustic and magnetic signatures of all ships, from carriers to destroyers, from mine hunters to frigates, from support ships to patrol craft. Remember, no ship, which has hit a mine knew the mine was there. The old argument “I’m not taking my ship where there are any mines” just doesn’t hold water in a littoral environment. That might be true if we had perfect intelligence. But this has not been demonstrated in the past, nor is it likely in the future. In addition, objectives of force projection and assuring access may require a breakthrough under time constraints where 100% probability of lane clearance is not possible. Ignorance of current ship acoustic and magnetic signatures and safe standoff distances to mines may nearly guarantee an eventual catastrophic mine encounter.

The Requirement

Fortunately, for the Fleet, there are initiatives being considered that will correct this deficiency. OPNAV Instruction 8950.2 is currently being revised and updated to reflect the current threat of influence sea mines exploiting acoustic, electric field, and pressure signatures, not just the magnetic signature. The revision will serve to stand up a requirement for signature control and to provide information like that represented in Figure 2 for every deploying ship, which should also include our forward deployed prepositioned black hulled MPSRONs.

We must now implement point-defense for ships against sea mines through a comprehensive Ship Susceptibility Reduction Program consisting of four basic elements. The four elements: signature measurement, susceptibility assessment, deficiency correction, and signature control awareness, can attain a significantly improved mission readiness in a prevalent sea mine environment and promote/enhance safe access when needed.

Future Hope

We can and must do better to assure access, and to assure Fleet readiness. Attention to acoustic and magnetic signature control has been done by submariners for decades. It is time to take those lessons from the brethren in the “Silent Service” and incorporate it in future ship designs. If done in the design phase, cost could be transparent to the overall shipbuilding budget.

A Signature Control Program for MCM/MHC ships as depicted in Figure 3 has been budgeted by OPNAV N75 for FY 03. Many senior naval officers have been briefed on MIW and ship signature control and concur with the need, importance, and criticality of signature control from the sea mine perspective. But, unfortunately, there is still little money or priority for this capability.

The “Hidden Pillar” of OMCM—signature control—will remain hidden, continuing the susceptibility of the Fleet to exploitation by sea mines, and access likely denied, unless CFFCs 27 1430Z Jul 01 message on mainstreaming mine warfare is heeded and backed up with taxpayer dollars to provide a Signature Control Program with adequate acoustic and magnetic ranges. Otherwise, the Fleet may remain blind to a prevalent known increased threat, and the next influence sea mine may well sink a ship and cause significant loss of life. Continued failure to incorporate MIW signature control lessons learned from USS Princeton (Congressionally mandated eight years ago) will allow the enemy to exploit Fleet signatures, and negate the billions of dollars spent to achieve the Navy’s long stated goal of “Assured Access.”


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