Planting mines by submarine has an advantage over surface craft and aircraft, as mining operations can be done in secrecy and at a great distance from the homeport. A disadvantage of using submarines is that they can carry only a limited quantity of mines. In addition, submarines must avoid the mined area for the armed life of the mines. Therefore, it would be unsafe for submarines to enter and reseed an established minefield.

SURFACE-LAID MINES

The surface-craft method of laying mines is used where secrecy is not of primary importance. This form of minelaying is usually performed by high-speed minelayers. A surface minelayer can carry a large number of mines and can lay a large minefield in a relatively short time. At the time of this writing, the Navy has no surface minelayers in commission. However, the Navy does have several types of cargo ships that can be used to surface launch the Mk 60 mine.

MINEFIELD TYPES Fundamentally, mining should achieve its objective by making an area unsafe for passage of traffic. A minefield is an application of the capability of available mines and delivery vehicles to the problem at hand. Mines are not normally used just one at a time, but are used as a group to establish a minefield. Each minefield is planted for a defensive, protective, or offensive purpose. The design of a minefield depends on the purpose of the field, including (1) the expected enemy traffic, (2) the type and number of mines available, (3) the field's geographic location, (4) the amount of enemy countermeasures to which it will be subjected, and (5) the laying agents to be used.

DEFENSIVE MINEFIELDS

Defensive minefield are laid in extra-territorial or neutral waters, and are designed to hold back the opposition. We try to keep the enemy guessing at all times about our minefield, but in some cases, the defensive field is well advertised so that the enemy will know it is there. The field then becomes more effective, since the enemy may decide not to enter those waters because of the existing danger. We still use the mined waters for our own shipping, and we supply accurate charts to friendly ships that need them. Some of the reasons defensive minefield are used are to

*provide permanent defense of harbors and anchorages,

protect coastal shipping lanes from seaward attack,

protect assembly points for convoys,

provide submarine traps, and

protect against invasion.

PROTECTIVE MINEFIELDS

Protective minefield are laid in friendly territorial waters to protect our own and friendly terminal areas, shores, and their approaches. Therefore, the fields differ in purpose as well as in the likely degree of enemy opposition.

OFFENSIVE MINEFIELDS

Offensive minefield take the action to the enemy. They are planted in enemy-held or disputed waters to disrupt enemy shipping by destroying or damaging the enemy's ships or by making areas unusable because the threat of losses is too great. In contrast to defensive and protective mining, offensive mining poses the most direct threat to the enemy and, once completed, none to own forces. Whenever possible, offensive mining should commence early in the conflict with the most appropriate countermeasuresresistant mines available for two reasons: (1) to present an early danger, and (2) to lessen the need for hazardous early replenishment. The United States used an offensive minefield very effectively in Haiphong Harbor during the Vietnam War.