Missile Impact Location System

Design and development was by American Telephone and Telegraph Company (AT&T), with its Bell Laboratories research and Western Electric manufacturing elements and was to an extent based on the company's technology and experience developing and deploying the Navy's then classified Sound Surveillance System (SOSUS).

[2][3][4] MILS took several forms and each had a unique configuration based on purpose and local water column and bottom conditions.

The target arrays were bottom fixed hydrophones connected by cable to the shore stations.

[1][2][note 2] The target arrays received the acoustic effect of an object's impact with the ocean surface then by the effect of an explosive charge with location calculated by the difference in arrival times at the hydrophones arranged to form a rough pentagon with a sixth hydrophone at the center.

[5] A particular advantage of the pentagon configuration was that a rapid approximate position could be calculated on simple time sequence of the acoustic wave at the hydrophones with detailed analysis producing a more exact location.

Since the downrange islands did not offer ocean bottom at that depth in the required configuration a system of suspended hydrophones was used.

PMR began installation of a Pacific MILS to support Intermediate Range Ballistic Missile (IRBM) tests with impact areas northeast of Hawaii.

Accuracy was improved by pre test calibration by a ship precisely located by a fixed transponder field releasing SOFAR bombs.

Those included both intentional experiments and acoustic incidents in which they were tasked after the fact to examine records.

A source ship, Cory Chouest, near Heard Island in the Indian Ocean generated signals that were received at Ascension at some 9,200 km (5,700 mi; 5,000 nmi) distance after passing around Africa.

Three hydrophones correlated acoustic arrivals with the time and estimated location of the double flash detected by the Vela satellite.

[21] SMILS was exclusively used to support the Navy's fleet ballistic missile programs under the Strategic Systems Project Office with much of the information classified.

[22] The sonobuoy type impact area used a sonobuoy field, typically four rings 3 nmi (3.5 mi; 5.6 km) apart with outside diameter of 20 nmi (23 mi; 37 km), sowed by aircraft and the reference transponder field for geodetic position.