SDU-5/E Distress Marker Strobe Light was used by the U.S. military since late 1960s. It was originally issued with various aircrew survival vests and life preservers. It was waterproof and produced an intermittent flash of light visible for beyond five miles. Accessories include a carrying pouch, flash guard / blue filter (FG1C), and various types of lens covers. It was later replaced by the MS-2000 strobe and other modern strobes.