tripods to attack vertical lift aircraft on landing and troops on disembarking from them.
Mine density affects the ability to find and clear or neutralize mines in a short time, and therefore influences both the kind and amount of countermine resources needed. Mine densities in deep water might be measured in terms of only a few mines per square mile. In shallow water and surf zones, there might be a dozen mines in the 50-yard pathway that must be cleared for an assault force to move ashore. Scattered antipersonnel and antitank mines on land may be as dense as dozens per acre; buried antitank mines on roads or elevated antiaircraft mines in landing zones will be less dense on average because their effective areas are larger and because they tend to be placed at strategic locations. However, they may be clustered at strategic locations.
Obstacles to landing on the beach could be reinforced concrete blocks of various shapes and sizes; crossed, welded, and embedded railroad rails; embedded telephone poles; or concertina wire and razor tape. If the obstacles do not actually damage the vehicles and injure the personnel who attempt to cross them, they can stop would-be penetrators for long enough to make them targets for defending fire.
Eliminating mines and obstacles from the path of an invasion requires operations by mine sweeping and clearing ships and helicopters, by special operations forces, and by the landing forces themselves in the surf and landing zones. Such capabilities exist in the mine countermeasures and minehunter class (MCM-1 and MHC-1) ships, the minehunter (MH)-53E helicopter, and various towed sonars and SEALs (sea, air, land teams), all of which can find and clear or neutralize mines in depths of up to 20 ft. SEALs have clandestine capabilities to locate, classify, tag, and place explosive charges on mines at shallower depths, in 12-ft depths or less, and to prepare explosive charges to destroy beach obstacles. The amphibious assault ship Inchon (LPH-12) is being refitted as a mine countermeasures command, control, and support ship (MCS) for use by the Mine Countermeasures Group Commander in an amphibious force.
All such operations take time, and stealth must be preserved in the vicinity of landing beaches and zones. The longer the mine clearance operations take, the greater the chance that the landing force's stealthy cover and thus the element of surprise will be “blown” and that new mines and obstacles will be emplaced by a resourceful enemy. The very shallow water and surf zones, from about 12-ft depth in through the craft landing zone on the beach, are especially difficult to deal with in this respect.
The time taken to overcome mines and barriers can deny surprise to the landing force. The Marines have focused attention in their requirements process on the idea of “in-stride” mine clearance in the shallow water and surf zones, so that the landing forces in these zones can simply move at the time and speed