MILS.
As missile technology was being developed in the 1950's and '60s, the 'powers that be' wanted to be sure that the missiles that were being developed were going to be able to accurately hit their intended target. With missiles that had a range of up to 1,500 miles, and which on occasion 'went wrong', and either exploded themselves into oblivion, or were purposely aborted, it was felt unwise to conduct testing over land areas. People weren't too keen to have this kind of 'hit or miss', 'trial and error' nonsense going on in the skies overhead, while they went about their daily business. The obvious solution was to shoot these test missiles over the ocean. No paint has yet been developed that could be used to paint a bullseye on the ocean surface, so some other means of observing the accuracy was required.
The first generation of missile accuracy testing was called MILS - short for Missile Impact Location System. In the early days of missile development, accuracy tests were conducted by aiming a missile at a specific location in the Atlantic Ocean off the Leeward Islands - about 1000 miles from Cape Canaveral. An array of hydrophones had been placed in the ocean around this target area, and their positions accurately determined. The missiles were aimed at the centre of this array of hydrophones. The missile warhead contained a SOFAR bomb, which was released on impact with the ocean, and would sink to the depth of the Sound Channel Axis before exploding. Based on the arrival time of the signal at each hydrophone, the impact point (and hence the accuracy of the missile) could be determined.
As time passed, and the range of the missiles increased, the system was expanded to include other hydrophones scattered around the Atlantic basin, which could be used to determine with reasonable accuracy the impact location of the SOFAR bomb from a missile aimed at just about anywhere along the Atlantic Missile Range. The Atlantic Missile Range started at Cape Canaveral, and headed approximately South East over open water towards Ascension Island, and beyond.
The accuracy of the early missiles was not great - perhaps 2 - 3 miles, so using the hydrophones scattered around the Atlantic (which could determine the location of a SOFAR bomb to a circle of probable impact of less than 100 yards) was 'good enough for Government work'.
This is the system that was used for the testing of all versions of the Polaris missile, and the early Poseidon models.
But as the missile guidance systems became more accurate, a more accurate method of calculating the impact point became necessary. Thoughts of installing target hydrophone arrays (like the one near the Lesser Antilles) along the length of the Atlantic Missile Range were never entertained, being considered too expensive to install and maintain, and not flexible enough for the developing missile technology.
So SMILS was born!
As time passed, and the range of the missiles increased, the system was expanded to include other hydrophones scattered around the Atlantic basin, which could be used to determine with reasonable accuracy the impact location of the SOFAR bomb from a missile aimed at just about anywhere along the Atlantic Missile Range. The Atlantic Missile Range started at Cape Canaveral, and headed approximately South East over open water towards Ascension Island, and beyond.
The accuracy of the early missiles was not great - perhaps 2 - 3 miles, so using the hydrophones scattered around the Atlantic (which could determine the location of a SOFAR bomb to a circle of probable impact of less than 100 yards) was 'good enough for Government work'.
This is the system that was used for the testing of all versions of the Polaris missile, and the early Poseidon models.
But as the missile guidance systems became more accurate, a more accurate method of calculating the impact point became necessary. Thoughts of installing target hydrophone arrays (like the one near the Lesser Antilles) along the length of the Atlantic Missile Range were never entertained, being considered too expensive to install and maintain, and not flexible enough for the developing missile technology.
So SMILS was born!