Offensive Mine Warfare - Operational Usage

We previously reviewed the Navy’s inventory of mines (see, "Offensive Mine Warfare") and noted that there are only two active versions:

• Quickstrike – converted general purpose bombs of 500, 1000, and 2000 lb sizes
• SLMM (Submarine Launched Mobile Mine) – modified Mk37 torpedo

We further noted that the delivery options for these mines are quite limited.  B-1 and B-52 bombers have mine laying capability but rarely train for the mission.  Submarines theoretically have the capability but have little capacity and apparently do not regularly train for the mission.

Mk 65 Quickstrike Mine Loading Onto A B-1 Bomber

How does this matter?  Well, that brings us to the operational employment of mines.  In order to understand their employment, we need to have an understanding of their historical use.  Without attempting to document a comprehensive listing, here are some notable historical uses by the US military.

In WWI, over 6000 mines were laid as part of the North Sea Mine Barrage, intended to inhibit U-boat movement into the Atlantic convoy lanes.  A US Navy group of ten converted commercial ships took part in the effort, aided by the Royal Navy.

Defensive minefields were laid up and down the east coast of the US and into the Caribbean during WWII.  Navweaps website states that 20,000 mines were laid defensively in US waters alone (2).  As far as is known, no enemy ship was sunk by the approximately 20,000 mines used in defensive minefields placed in US waters (2).

Also in WWII, US submarines planted mines in Japanese harbors and shipping lanes.

“[During WWII] US submarines planted a total of 576 Mark 12 mines and 82 Mark 10 mines in 36 fields. Of these, 421 mines planted in 21 of the fields sank 27 ships of about 63,000 tons and damaged 27 more of approximately 120,000 tons.” (2)

By 1945, the Army Air Force was devoting considerable resources to the mining role, with 80 to 100 B-29s based at Tinian being used to mine the home waters around Japan. These B-29s could carry seven 2,000 lbs. (907 kg). or twelve 1,000 lbs. (454 kg) mines. Starting in March 1945 and continuing until early August, 4,900 magnetic, 3,500 acoustic, 2,900 pressure and 700 low-frequency mines were laid. These mines sank 294 ships outright, damaged another 137 beyond repair and damaged a further 239 that could be repaired. In cargo tonnage, the total was 1.4 million tons which was about 75% of the shipping available in March 1945.

“Between January and March 1945, B-29s also closed the approaches to Singapore, Saigon and Camranh Bay harbors by magnetic mining.” (2)

Smaller WWII Aircraft were also used to lay mines.

“Avenger and Ventura aircraft could carry a single mine and in 1944 Avengers closed Palau harbor by mining the entrances. They then sank all 32 ships in the harbor with conventional bombs and torpedoes. A total of approximately 100 ships were sunk or badly damaged in the Pacific during the war by mines laid by Navy aircraft.”

This was a classic example of sealing the escape route and then destroying the trapped vessels at leisure.

We see, then, that a major conflict could be expected to require many tens of thousands of mines.  I can’t recall ever seeing an inventory summary of how many mines the US Navy has but I strongly suspect it’s not a large amount. 

Further, note that mine laying objectives are two-fold: 

• One, is an offensive minefield intended to close enemy harbors, approaches, and navigational chokepoints.

• Two, is a minefield intended to provide defensive protections around friendly harbors or invasion site approaches.

As a bit of a sidenote, here are some interesting examples of mine laying vessels used by the Navy in WWII.

• The Navy developed a dedicated mine laying destroyer in WWII, the Robert H. Smith class, which was a variant of the Sumner class destroyers.  Twelve ships were built in late 1943 and early 1944.  Mine tracks ran along both sides of the ship and each track could hold 60 mines.  The mines were released over the stern, similar to the way depth charges were dropped (1).  Astoundingly, none of the ships ever laid a mine!

• The Navy did utilize a converted cargo ship, USS Salem CM-11, to lay 202 mines of Casablanca in late December 1942.  Salem also laid 390 mines off Gela, Sicily in July, 1943 in support of the Sicily invasion.

• USS Weehawken, CM-12, originally a 1920 car ferry, was converted to a mine layer.  The ship laid defensive mine fields of Casablanca in December 1942 along with USS Salem and USS Keokuk.  Following that, she laid minefields off Gela, Sicily in July 1943.

• USS Keokuk, CM-8, was also a conversion of a commercial ship built in 1914.  Wiki suggests that the ship engaged in mine laying along the Atlantic coast of the US during the summer of 1942.  The ship also participated in the mine laying off Casablanca and Sicily along with Salem and Weehawken.

• USS Terror, CM-5, was the only purpose built Navy minelayer of WWII.  She laid defensive mines off Casablanca in December 1942.  The ship also operated in the Pacific, laying mines in the Pacific Marshall Islands in March and April 1944 and around Ulithi in September of 1944.  She also acted as a tender for numerous small craft engaged in mine laying and mine sweeping.

• Several Clemson class 4-stacker destroyers were converted to mine layers during WWII.

We see then, that mine laying has, historically, never been given much priority in terms of developing dedicated mine laying vessels.  When the need arose, the Navy converted commercial vessels or adapted destroyers already in production.  This can be interpreted one of two ways:

1. The Navy has failed to recognize the importance of mine laying and is continually caught short when the need arises or,

2. Mine laying is a simple and generic enough exercise that there is no need to maintain dedicated vessels and when the need arises, any suitably sized vessel can be adapted to the task.

I tend to think it’s a combination of the two with a leaning towards the relatively undemanding nature of mine laying and the underlying economics of conversion versus maintenance of a dedicated mine laying force.  Of course, this only applies to mine laying in relatively uncontested areas.  Mining contested areas like enemy home waters requires either stealth (submarine mine layers) or stealth/speed (aircraft) in order for the laying vehicle to survive.  This suggests the need for maintaining a dedicated mine laying vehicle for contested areas.  Converted vehicles simply will not have the stealth and/or speed necessary for the task.

Let’s return, now, to the operational aspects of offensive mine warfare.

History tells us the kinds of mining that will be required.  So what kind of targets/areas should we be planning for in a major war?

Iranian harbors – a relative handful of mines could effectively shut down Iran’s entire navy (such as it is) and commercial shipping.

NKorean harbors – war with NKorea will be a land and air war.  I can foresee no reasonable need to conduct an amphibious operation but the ability bottle up NKorea forces and effectively blockade Russian and Chinese resupply vessels would be worthwhile.

Russian harbors, approaches, and navigational chokepoints especially those used by the Russian sub fleet, if mined, would deal a critical blow.  Mining of the so-called SSBN bastions would deny Russia the use of its ballistic missile submarines and completely disrupt one of their major strategic foundations.

Chinese harbors and navigation chokepoints are particularly susceptible to mining.  The narrow waters and sea lanes between the first island chain islands provide ideal opportunities to restrict Chinese submarine and surface ship movements and island resupply efforts.  An effective mine laying program would largely bottle up China’s fleet and remove at least one aspect of the A2/AD zone.

In summary, the patterns of use of offensive mine warfare are clear as is the need in future conflicts.  What is far less clear is the capacity of the US Navy to wage effective offensive mine warfare given the lack of mines (inventory), the dearth of mine laying platforms, and near total disregard for offensive mine warfare tactics and training.  As is so often the case, the US Navy is focused on the big, shiny toys and is neglecting a far more powerful and effective weapon.

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(1)Destroyer History Foundation website,

http://destroyerhistory.org/sumner-gearingclass/dm/

(2)NavWeaps website,

http://www.navweaps.com/Weapons/WAMUS_Mines.php