The Klein System 4900 Side Scan Sonar was put to good use on the West Coast of Scotland in support of diving operations on a sea inlet once referred to as the Secret Loch.
In World War II, British engineer Sir Barnes Wallis invented the bouncing bomb that was designed to skip over the surface of a stretch of water, avoiding anti-torpedo nets, before sinking directly next to a dam wall or battleship target. The initial bombs, codenamed Upkeep, were used successfully against the Ruhr dams in Northern Germany.
Developed in parallel with the Upkeep bombs were a smaller spherical bomb codenamed Highball, and these were specifically designed as an anti-ship weapon – particularly with the German battleship Tirpitz in mind as a potential target. The Highball was destined to carry a 500lb charge in a cylinder contained in a 35in sphere and dropped at high speed from a modified Wellington or Mosquito bomber.
Testing of the weapon took place at Chesil Beach and Reculver in England but in May of 1943 tests were carried out against a target ship, a former French battleship, the dreadnought Courbet, which was moored specifically for the tests in Loch Striven.
Extending off the Firth of Clyde just North of the Isle of Bute, Loch Striven forms a narrow sea inlet about 8 miles long and during World War II the upper reaches of the loch were used for training operations on midget submarines as well as the Highball program. The area was highly restricted and the authorities went to some effort to obscure the entrance to the inlet to keep the covert activities secret.
The X-Craft midget submarines were armed with two side-cargo explosive charges containing 4,400lbs of Amatol that would be deployed under the target vessel and training operations on this method were also carried out in Loch Striven.
The System 4900 side-scan was deployed from the Aspect Surveys vessel Vigilance and operated by personnel from GSE Rentals who had provided the winch, cable and ancillary support for the project. An initial pass through the centre channel of the Loch revealed the seafloor was made up of a relatively featureless area save for extensive trench-marks and scarring presumably caused by the anchor chains used by large cargo container traffic that at one time used the loch as a safe haven during poor weather.
On approaching the area nearer the location of the target ship it was discovered that one or two Highball devices had clearly fallen short of the Courbet and it was suggested that this may have been as a result of the poor marking of the target area during the initial tests which apparently had confused the bomber pilots on approach. As it passed closer, the side-scan presented images of side-cargo charges deployed during X-Craft tests.
Arriving at the target area it quickly became apparent that there was a more dense scattering of Highballs in an around sections of anchor chain that had been cut and discarded with their anchors still in place as the French target vessel was towed away for scrap after the war.
Survey operators were able to take full advantage of the 4900s to provide high definition images for classification to 75 m per side at 900 kHz.
The data produced was used to good effect when the diving operation needed to clarify which targets would be suitable candidates for recovering the Highball device and the plan is to display the recovered artifacts at the Brooklands Museum in Surrey and the de Havilland Aircraft Museum in Hertfordshire.