Moored - Aircraft laid


♦ Mk 56

Mk 56 is a 2000-lb aircraft-laid moored mine (22.4 in x 114.3 in), with a 360-lb charge (HBX-3).

Mk 56 could be set to moor at an adjustable depth (30-4-80 ft). Compared to earlier air-laid moored mines, it has an in-creased range of planting depths and a variable mine-case release timer. It enjoys greater target selectivity through the use of a new total-field magnetic-influence mechanism that can be adjusted to respond equally well to slow or fast targets. Minimum sensitivity is about 20% that of the earlier Mk 10. Like the air-laid Mk 50 series, Mk 56 is easier to assemble because it employs modular components. It has a ship counter (1-30 counts); Mk 10 has none, and Mk 36 has 1-10. Variable planting depth is 150-600 ft, compared to 100-400 ft for Mk 36. Assembly time is 2 hr, compared to 6 hr for Mk 10 and 8 hr for Mk 36. Mk 52 arms in 1 hr, compared to 65-180 min for Mk 10. When Mk 52 appeared in 1957, it was described officially as a realistic threat to submarines, whereas the earlier Mk 36 represented only a limited threat.

The Service Mine Mk 56 is an explosive-loaded (HBX-3 fill) moored mine operationally planted by personnel flying B-52H Stratofortress, F/A-18A/D Hornet, and P-3C Orion aircraft.

This 2,000-pound mine consists of an anchor, mechanism section, explosive section, and flight gear. Although intended primarily as an anti-submarine weapon, it can also be used effectively against surface craft. The mine employs a magnetic firing mechanism, which uses a total-field magnetometer as its influence detector. Unlike earlier search coils which responded to changes in only one component of a ship’s magnetic field, the Mine Mk 56’s magnetometer responds to changes in magnitude of the total background field. The mechanism/explosive sections are painted brick red and the anchor is painted black.

Six OAs exist for the Service Mine Mk 56: OAs 05, 06, 09, 10, 11, and 12. Minefield planners use these OAs to provide the characteristics necessary to meet a specific operational requirement such as the need to employ a particular flight gear option, the need for a special auxiliary device such as the gas generator used to free the mine from mud, etc. The possible assembly variations are too numerous to mention here.

Building Mk 56s

The Laying Mine Mk 56 is a recoverable, inert-loaded mine identical in size and weight to its Service mine counterpart. It is designed solely for training aviation personnel flying B-52H, F/A-18A/D, and P-3C aircraft in the techniques of carrying mines and planting minefields.

This mine consists of a non-functional anchor since it does not separate and moor the mine’s mechanism section. It also has an inert-loaded explosive section, an arming device simulator, and functional flight gear. For MMS Mk 5 recovery, a marine mammal recovery attachment is installed on the arming device simulator. The mechanism and inert-loaded explosive sections are painted either white with orange stripes or orange with white stripes and the anchor remains black.

Two OAs (05K and 06K) exist for the Laying Mine Mk 56. They differ only in that OA-06K calls for the installation of a Fairing Mk 21 consisting of an aerodynamic nose and nose piece.

Mk 56 was released for production in 1960 and became operational in 1966;


♦ Mk 57

Mk 57 is a similar submarine-laid magnetic moored mine (2059 lb, 340 lb of HBX-3, 1 in x 121.1 in), for water up to 200 fathoms deep. Mk 56 uses a total-field magnetic exploder and has a stainless-steel nonmagnetic case.

Mk 57, the submarine-laid version of Mk 56, with a fiberglass case, was released for production at the same time and became operational in 1964. In each case, the delay was caused by a lack of funding for production at the time.




Derick S. Hartshorn - 2009-present
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