craters, and the resulting channel would be partially filled with debris-possibly including still-active mines. The bottom and sides of the channel in these cases would be irregular.
Sequenced explosions also lack the dynamic synergism of simultaneous detonation that creates a channel of relatively uniform width with a small end lip. Water flow, in the sequenced case, will occur after each explosion to smooth crater edges, but the final explosion at the end will not benefit from the previous ones to reduce its lip. It is unlikely that sequential explosions would create as deep a channel as simultaneous detonation of the same amount of explosive material.
A slow sequenced-explosion experiment has, in fact, been done at the Navy's Panama City Laboratory Test Site, in which a first explosion on the bottom (at water depth of about 5 feet) pushed aside mines and obstacles, and after things had settled a second explosion, closer to the edge of the moved mine-obstacles pattern, was set off to push them out some more. It should be possible to continue this pattern to form a cleared channel; this could be continued into shallow water and up the beach, by exploding sequentially so that ejecta are always thrown away from the craters previously formed, but, as noted, this is a slow process.
The excavation accomplished by simultaneous detonation results mainly from the explosives' gas bubble; the bubble growth time, of the order of several hundredths of a second, sets the bounds on the degree of simultaneity required. A 1992 study on mine countermeasures conducted by the Naval Studies Board1 suggested that simultaneity to within ≤ 0.01 seconds is required.
All this assumes that the measure of effectiveness for channel clearance is mine removal. If mine destruction were the measure, simultaneous detonation would offer the advantage only of smoother final channel shape, and a small end lip. Among the impediments to breaching the surf and craft landing zones are the durability of some of the mine types that are typically deployed in near-shore waters and the consequent difficulty of destroying them.