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Title:AS PROJECTOR MARK 10 (HEDGEHOG) [Main Title]
Film Number:ADM 238-7
Summary: US instructional film on the use of the Hedgehog (Mark 10) AS projector.
Description: The 'Mousetrap' and 'Hedgehog' projectors enable a group of fast sinking, contact fused depth charges to be thrown ahead of the ship, while the target is still under SONAR location. Graphics illustrate the advantages of an ahead-thrown attack. Illustration of the circular pattern produced by the Hedgehog, and the principles of proper pattern placement, involving compensation for the ship's movement, and last minute changes in the scheme of attack. Distortion of the pattern in proportion to the degree of the offset from dead-ahead, and the desirability of a dead-ahead attack for good pattern shape. Depth charge flight and sinking times to various depths. Graphics illustrate the advantages of fast sinking and contact explosion - the charge is effective "regardless of target depth". The film ends by summarising the combined advantages of the Hedgehog projector, and recapitulating the correct attack procedure. A concluding section notes that the use of the Hedgehog avoids the disturbance of the water created by stern dropped depth charges, which can make it difficult to re-establish SONAR contact with the target.